Multitube reactor, vapor phase catalytic oxidation method using the multitube reactor, and start up method applied to the multitube reactor

ABSTRACT

A multitube reactor, wherein tubes having smaller tolerance between a nominal size and actual sizes are used as reaction tubes to stably perform a high yield reaction for a long period, a catalyst is filled into the reaction tubes so that the catalyst layer peak temperature portions of the reaction tubes are not overlapped with the connection sites thereof with baffles to effectively prevent hot spots from occurring and stably perform a reaction for a long period without the clogging of the reaction tubes, a heat medium and raw material gas are allowed to flow in the direction of a countercurrent and a specified type of catalyst is filled into the reaction tubes so that activity is increased from the inlet of the raw material gas to the outlet thereof to prevent the autooxidation of products so as to prevent equipment from being damaged due to the reaction, and, at the time of starting, gas with a temperature of 100 to 400° C. is led to the outside of the reaction tubes to increase the temperature of the reaction tubes and, a heat medium, which is solid at the room temperature, is heated to circulate to the outside of the reaction tubes to efficiently start up the reactor without affecting the activity of the catalyst.

TECHNICAL FIELD

The present invention relates to a multitube reactor applied to a methodof producing (meth)acrolein and/or (meth)acrylic acid by oxidizingpropylene, propane, isobutylene, isobutanol, or t-butanol with amolecular oxygen-containing gas, a vapor phase catalytic oxidationmethod using the multitube reactor, and to a start up method applied tothe multitube reactor.

BACKGROUND ART

A conventional multitube reactor is equipped with a plurality ofreaction tubes having a catalyst packed therein and a plurality ofbaffles inside a shell for feeding and circulating inside the shell afluid for heat removal (hereinafter, referred to as “heat medium”)introduced into the shell. A raw material gas fed inside the reactiontubes reacts in the presence of the catalyst inside the reaction tubes,to thereby generate heat of reaction. The heat of reaction is removed bya heat medium circulating inside the shell.

When differences of inner volumes among the plurality of reaction tubesequipped inside the shell is large, amounts of the catalyst packedinside the reaction tubes are irregular and a scatter arises. As aresult, a flow rate of the raw material gas fed or a retention timediffers among the reaction tubes, thereby becoming a factor causingyield reduction of a target product and reduced catalyst life. Further,a localized abnormal high-temperature site (hot spot) may form in thereaction tubes provoking a reaction out of control, thereby causing aproblem of inhibiting a continuous operation.

Further, in a multitube reactor provided with the baffles, the heatmedium does not flow at all in a portion where the baffles and thereaction tubes are fixed to each other when the baffles and the reactiontubes are fixed through welding, flanges, or the like. A reactor inwhich outer walls of the reaction tubes and the baffle are not fixedalso exists, but the amount of the heat medium flowing through thisclearance is limited. The following problems arise in a vapor phasecatalytic oxidation method using a fixed bed multitube heat-exchangertype reactor as described above.

There is a state of poor heat removal in the reaction tubes in a portionwhere flow of the heat medium is insufficient inside the shell. Alocalized abnormal high-temperature zone (hot spot) may form in thereaction tubes which are in a state of poor heat removal, possiblyresulting in a reaction out of control. Further, a reaction may notbecome out of control, but problems arise including ease of clogging thereaction tubes, yield reduction of the reaction product gas,deterioration of the catalyst life, and inhibition of a stable operationfor a long period of time.

Many methods of suppressing hot spot formation have been proposed forthe multitube reactor used in a vapor phase catalytic oxidationreaction. For example, JP 08-092147 A discloses a method of providinguniform heat medium temperature by: setting a flow direction of areactant gas guided to a reactor and that of the heat medium inside ashell in a countercurrent; allowing the heat medium to flow furtherupward in a meandering way using baffles; and adjusting temperaturedifferences of the heat medium from an inlet of the reactor to an outletthereof within 2 to 10° C. or less.

The multitube reactor generally consists of a plurality of tubes(bundle) arranged vertically, and thus a process fluid flow can beupflow or downflow by allowing a process fluid to flow from an upperportion or lower portion of the reactor. The heat medium can also be fedto the shell from the upper portion or lower portion thereof.

Therefore, the multitube reactor is classified into two types similar toa general shell and tube heat exchanger: a concurrent type allowing theprocess fluid and the heat medium to flow in the same direction; and acountercurrent type allowing the process fluid and the heat medium toflow in opposite directions.

Further, the multitube reactor may be classified into the followingtypes considering the directions of the fluids: 1) a concurrent type ofdownflow process fluid/downflow heat medium; 2) a concurrent type ofupflow process fluid/upflow heat medium; 3) a countercurrent type ofupflow process fluid/downflow heat medium; and 4) a countercurrent typeof upflow process fluid/downflow heat medium.

Proposed in JP 2000-093784 A is a method of suppressing hot spotformation by: allowing a raw material gas and a heat medium to flow indownward concurrent; and preventing a gas reservoir free of the heatmedium. Further, the method allows an exchange of a catalyst in avicinity of a catalyst layer inlet alone where most easily deterioratesby: feeding the raw material gas from an upper portion of a reactor; andallowing the raw material gas to flow downward inside the catalyst layerof reaction tubes.

However, the heat medium and the process fluid move in a concurrentaccording to the method, and gas temperature in an outlet portion of thereactor increases. Thus, the method has a fault that high concentrationof a product (meth)acrolein easily causes an autooxidation reaction(autolysis reaction).

Further, with respect to the upflow, in a method of allowing the processfluid and the heat medium to flow in a concurrent, that is in the samedirection, heat medium temperature increases with heat of reaction.Thus, high temperature at a process outlet causes autooxidation at thereactor outlet easily. The autooxidation reaction results in problems ofa combustion reaction of the product, equipment breakdown due totemperature increase, and yield reduction.

Proposed is a method of preventing autooxidation for a purpose ofpreventing temperature increase, by providing a cooling zone or heatexchanger in a downstream of a reaction portion for decreasing gastemperature. However, in a concurrent, heat medium temperature in thevicinity of the reactor outlet and process gas temperature in an outletportion are high. Thus, an amount of heat removal becomes large and acooling portion (cooling zone and heat exchanger) enlarges, therebybecoming disadvantageous in point of cost.

Further, even if a significant autooxidation reaction is not caused, anautooxidation reaction is caused by a part of a product, which arises aproblem of yield reduction of a target product as a whole.

Further, in a shell-tube type reactor circulating a heat medium which issolid at normal temperature, there is a necessary to maintain the heatmedium at temperature of the solidifying point or above to ensurefluidity thereof for circulating the heat medium inside the reactor.

JP 2001-310123 A discloses a-reactor start up method for a multitubereactor having reaction tubes, an introducing port of a fluid flowingoutside reaction tubes, and a discharging port thereof for removing heatgenerated inside the reaction tubes, the method being characterized byincluding: heating reaction tubes by introducing a gas havingtemperature of 100 to 400° C. in the reaction tubes; and circulating aheated heat medium through the outside of the reaction tubes. Further, agas not providing an effect when being mixed with a catalyst packed inthe reaction tubes or with a raw material gas (such as air) is selectedas the gas introduced to the reaction tubes.

However, a large volume of a high temperature gas is introduced to thereaction tubes according to the above-mentioned method, thereby changingan oxidation state of the catalyst. Therefore, catalytic activity andselectivity may be affected, possibly resulting in yield reduction orreduced catalyst life.

DISCLOSURE OF THE INVENTION

A first object of the present invention is to provide a multitubereactor for improving life of a catalyst packed inside the reactiontubes and for preventing yield reduction of a target product.

Further, a second object of the present invention is to provide a vaporphase catalytic oxidation method comprising: using the above-mentionedmultitube reactor; circulating a heat medium through the outside of thereaction tubes; and feeding a reaction raw material gas inside thereaction tubes packed with a catalyst to obtain a reaction product gas,in which hot spot formation can be effectively prevented, the reactiontubes are not clogged, an yield of a reaction product gas is high, acatalyst life is long, and a stable operation can be performed over along period of time.

Further, a third object of the present invention is to reduce processgas temperature at a product discharging port of the reactor in thevapor phase catalytic oxidation method using the multitube reactordescribed above.

Further, a fourth object of the present invention is to provide a methodwhich makes a reactor start up effectively without adversely affectingthe catalytic activity in a shell-tube type reactor of circulating aheat medium which is solid at normal temperature, the method beingapplied to a multitube reactor such as the above-mentioned multitubereactor.

The present invention provides a multitube reactor represented by thefollowing items (1) to (3) (hereinafter, may also be referred to as“multitube reactor of the present invention”) as a means for solving atleast the first object of the present invention.

(1) A multitube reactor comprising a plurality of reaction tubes havinga catalyst packed therein, and a shell equipped with the reaction tubesinside and into which a heat medium flowing outside the reaction tubesis introduced, wherein the reaction tubes are selected from tubes havingsame nominal outside diameter and same nominal wall-thickness, anoutside diameter tolerance of ±0.62%, and a wall-thickness tolerance of+19% to −0%.

(2) The multitube reactor comprising a plurality of reaction tubeshaving a catalyst packed therein, and a shell equipped with the reactiontubes inside and into which a heat medium flowing outside the reactiontubes is introduced, wherein the reaction tubes are selected from tubeshaving same nominal outside diameter and same nominal wall-thickness, anoutside diameter tolerance of ±0.56%, and a wall-thickness tolerance of+17% to −0%.

(3) The multitube reactor according to the above item (1) or (2), whichis used for production of (meth)acrolein and/or (meth) acrylic acid byoxidizing propylene, propane, isobutylene, isobutanol, or t-butanol witha molecular oxygen-containing gas.

Further, the present invention provides a vapor phase catalyticoxidation method represented by the following items (4) to (6) using themultitube reactor of the present invention for solving at least one ofthe second, third, and fourth objects of the present invention.

(4) A vapor phase catalytic oxidation method comprising: using themultitube reactor according to the above items (1) or (2), which furthercomprises baffles connected to the reaction tubes through connectingsites for changing a flow path of a heat medium introduced into theshell; circulating the heat medium through the outside of the reactiontubes; and feeding a reaction raw material gas inside the reaction tubespacked with a catalyst to obtain a reaction product gas,; wherein themethod comprises setting catalyst packing specifications in the reactiontubes so that catalyst layer peak temperature sites of the reactiontubes are not located at the connecting sites between the baffles andthe reaction tubes.

(5) The vapor phase catalytic oxidation method according to the aboveitem (4), wherein the method comprises: packing the reaction tubes witha Mo—Bi catalyst and/or Sb—Mo catalyst so that an activity increasesfrom a process gas inlet to a process gas outlet of the reaction tubes;allowing the heat medium and the process gas to flow in acountercurrent; and oxidizing propylene, propane, or isobutylene, and/or(meth)acrolein through vapor phase catalytic oxidation with a molecularoxygen-containing gas.

(6) The vapor phase catalytic oxidation method according to the aboveitem (4) or (5), wherein the method comprises: heating the reactiontubes through introduction of a gas having temperature of 100 to 400° C.outside the reaction tubes; and circulating the heat medium which issolid at normal temperature outside the heated reaction tubes to startup the multitube reactor.

Further, the present invention provides a vapor phase catalyticoxidation method (hereinafter, may also be referred to as “first vaporphase catalytic oxidation method”) represented by the following items(7) to (10) for solving at least the second object of the presentinvention.

(7) A vapor phase catalytic oxidation method comprising: using a fixedbed multitube heat-exchanger type reactor having a plurality of reactiontubes and baffles connected to the reaction tubes through connectingsites for changing a flow path of a heat medium flowing outside thereaction tubes; circulating the heat medium through the outside of thereaction tubes; feeding a reaction raw material gas inside the reactiontubes packed with a catalyst to obtain a reaction product gas,, whereinthe method comprises setting catalyst packing specifications in thereaction tubes so that catalyst layer peak temperature sites of thereaction tubes are not located at the connecting sites between thebaffles and the reaction tubes.

(8) The vapor phase catalytic oxidation method according to the aboveitem (7), wherein layers having different catalyst packingspecifications are provided with two or more catalyst in one reactiontube.

(9) The vapor phase catalytic oxidation method according to the aboveitem (7) or (8), wherein items for setting the catalyst packingspecifications comprise a type of catalyst, an amount of catalyst, aform of catalyst, a method for diluting the catalyst, and lengths ofreaction zones.

(10) The vapor phase catalytic oxidation method according to any one ofthe above items (7) to (9), wherein the method comprises oxidizingpropane, propylene, and/or isobutylene with molecular oxygen through thevapor phase catalytic oxidation method to produce (meth) acrylic acid.

Further, the present invention provides a vapor phase catalyticoxidation method (hereinafter, may also be referred to as “second vaporphase catalytic oxidation method”) represented by the following items(11) and (12) for solving at least the third object of the presentinvention.

(11) A vapor phase catalytic oxidation method comprises: using amultitube reactor which comprises: a cylindrical shell having a rawmaterial feed port and a product discharging port; a plurality ofring-shaped tubes arranged on an outer periphery of the cylindricalshell for introducing or discharging a heat medium into or from thecylindrical shell; a circulating device connecting the plurality of thering-shaped tubes one another; a plurality of reaction tubes restrainedby a plurality of tube plates of the reactor and comprising a catalyst;and a plurality of baffles provided in a longitudinal direction of thereactor and for changing a direction of the heat medium introduced intothe cylindrical shell; oxidizing propylene, propane, or isobutylene,and/or (meth)acrolein through vapor phase catalytic oxidation with amolecular oxygen-containing gas to obtain (meth)acrolein and/or(meth)acrylic acid,; wherein the method comprises,

-   -   packing a Mo—Bi catalyst and/or Sb—Mo catalyst in the reaction        tubes so that an activity increases from a process gas inlet to        a process gas outlet of the reaction tubes; and    -   allowing the heat medium and the process gas to flow in a        countercurrent.

(12) The vapor phase catalytic oxidation method according to the aboveitem (11), wherein the Mo—Bi catalyst is represented by the followinggeneral formula (I) and the Sb—Mo catalyst is represented by thefollowing general formula (II):Mo_(a)W_(b)Bi_(c)Fe_(d)A_(e)B_(f)C_(g)D_(h)E_(i)O_(j)   (I)(wherein, Mo represents molybdenum; W represents tungsten; Bi representsbismuth; Fe represents iron; A represents at least one type of elementchosen from nickel and cobalt; B represents at least one type of elementselected from the group consisting of sodium, potassium, rubidium,cesium, and thallium; C represents at least one type of element selectedfrom alkaline earth metals; D represents at least one type of elementselected from the group consisting of phosphorus, tellurium, antimony,tin, cerium, lead, niobium, manganese, arsenic, boron, and zinc; Erepresents at least one type of element selected from the groupconsisting of silicon, aluminum, titanium, and zirconium; O representsoxygen; a, b, c, d, e, f, g, h, i, and j represent atomic ratios of Mo,W, Bi, Fe, A, B, C, D, E, and O respectively; and if a=12, 0≦b≦10,0<c≦10, 0<d≦10, 2≦e≦15, 0<f≦10, 0≦g≦10, 0≦h≦4, and 0≦i≦30; and j is avalue determined from oxidation states of the respective elements); andSb_(k)Mo_(l)(V/Nb)_(m)X_(n)Y_(p)Si_(q)O_(r)   (II)(wherein, Sb represents antimony; Mo represents molybdenum; V representsvanadium; Nb represents niobium; X represents at least one type ofelement selected from the group consisting of iron (Fe), cobalt (Co),nickel (Ni), and bismuth (Bi); Y represents at least one type of elementchosen from copper (Cu) and tungsten (W); Si represents silicon; Orepresents oxygen; (V/Nb) represents V and/or Nb; k, l, m, n, p, q, andr represent atomic ratios of Sb, Mo, (V/Nb), X, Y, Si, and Orespectively; and 1≦k≦100, 1≦l≦100, 0.1≦m≦50, 1≦n≦100, 0.1≦p≦50,1≦q≦100; and r is a value determined from oxidation states of therespective elements).

Further, the present invention provides a method for starting up(hereinafter, may also referred to as “start up method of the presentinvention”) represented by the following items (13) and (14) for solvingat least the fourth object of the present invention.

(13) A start up method for a shell-tube type reactor having a system ofcirculating a heat medium which is solid at normal temperature, theshell-tube type reactor having reaction tubes, and an introducing portand discharging port of a fluid flowing outside the reaction tubes forremoving heat generated inside the reaction tubes, wherein the methodcomprises:

-   -   heating the reaction tubes through introduction of a gas having        temperature of 100 to 400° C. outside the reaction tubes; and        circulating the heated heat medium through the outside of the        reaction tubes.

(14) The start up method according to the above item (13), wherein theheat medium which is solid at normal temperature has a solidifying pointof 50 to 250° C.

Hereinafter, the present invention will be described in more detail.

<Multitube Reactor of the Present Invention>

A multitube reactor of the present invention is a multitube reactorequipped with a plurality of reaction tubes inside a shell of themultitube reactor, the plurality of reaction tubes being selected fromtubes having the same nominal outside diameter and the same nominalwall-thickness, an outside diameter tolerance of ±0.62% and awall-thickness tolerance of +19% to −0%, particularly preferably anoutside diameter tolerance of ±0.56% and a wall-thickness tolerance of+17% to −0%. The multitube reactor is suitably used in oxidizingpropylene, propane, isobutylene, isobutanol, or t-butanol with amolecular oxygen-containing gas.

In the multitube reactor of the present invention, the phrase “the samenominal outside diameter and the same nominal wall-thickness” means that“in a reaction tube, a nominal outside diameter and an actual outsidediameter are substantially the same and a nominal wall-thickness and anactual wall-thickness are substantially the same”. In addition, theabove-mentioned range of the tolerance is defined in the presentinvention as the range which represents “substantially the same”. Theactual dimensions of a reaction tube can be measured by means of aconventionally known method. The dimensions may adopt the measured valueat a given position or the average value of a plurality of measuredvalues.

An outline of the multitube reactor of the present invention will bedescribed with reference to FIG. 1.

Reference numeral 2 represents a shell of the multitube reactor, and theshell 2 comprises reaction tubes 1 a, 1 b, and 1 c each packed with acatalyst, the reaction tubes being fixed by both a lower tube plate 5 band an upper tube plate 5 a.

The reaction tubes 1 a, 1 b, and 1 c each have an inner diameter ofabout 20 to 40 mmφ, a wall-thickness of 1 to 2 mm, and a length of 3,000to 6,000 mm. A carbon steel tube or stainless steel tube is used as amaterial for each of the reaction tubes 1 a, 1 b, and 1 c.

The total number of the reaction tubes 1 a, 1 b, and 1 c equipped insidethe shell 2 varies depending on the amount of production of a targetproduct but: is typically 1,000 to 30,000. The arrangement of the tubesvaries depending on outside diameter sizes of the reaction tubes, butthe reaction tubes equipped inside the shell at intervals of 5 to 50 mmto establish a square arrangement or an equilateral trianglearrangement.

The above equilateral triangle arrangement is often used because thearrangement can increase the number of the reaction tubes 1 a, 1 b, and1 c equipped inside the reactor per unit area.

The outside diameter tolerance and wall-thickness tolerance of each ofthe reaction tubes used in the present invention are far more rigorousthan the tolerance of JIS or of ASTM, and such tubes that satisfy therigorous tolerances are used.

That is, each of the reaction tubes is desirably selected from tubeproducts having the same nominal outside diameter and the same nominalwall-thickness, an outside diameter tolerance of ±0.62% and awall-thickness tolerance of +19% to −0%, particularly preferably anoutside diameter tolerance of ±0.56% and a wall-thickness tolerance of+17% to −0%. In the multitube reactor of the present invention, all thereaction tubes equipped inside the multitube reactor preferably satisfythe above conditions. However, it is sufficient that at least 95%, morepreferably at least 99% of the tubes satisfy the above conditions.

The shell 2 has, at its top and bottom ends, inlet and outlet portions 4a and 4 b for a raw material gas Rg for a reaction, and the raw materialgas Rg flows through the reaction tubes 1 a, 1 b, and 1 c in an upwardor downward flow direction via the inlet and outlet portions 4 a and 4 bfor the raw material gas arranged on the top and bottom ends of thereactor. The flow direction of the raw material gas is not particularlylimited, but is more preferably a downflow.

In addition, a ring-shaped tube 3 a for introducing a heat medium Hm isarranged on the outer periphery of the shell 2. The heat medium Hmpressurized by a circulating pump 7 is introduced into the shell 2through the ring-shaped tube 3 a.

The heat medium Hm introduced into the shell 2 flows upward whilechanging its flow direction as indicated by arrows due to baffles 6 a, 6b, and 6 a equipped inside in the shell 2. During this period, the heatmedium Hm contacts the outer surfaces of the reaction tubes 1 a, 1 b,and 1 c to remove heat of reaction, and then returns to the circulatingpump 7 via the ring-shaped tube 3 a arranged on the outer periphery ofthe shell 2.

Part of the heat medium Hm absorbing the heat of reaction flows toward adischarge tube 8 b arranged on an upper portion of the circulating pump7 to be cooled by a heat exchanger (not shown). Then, the heat medium issucked again in the circulating pump 7 through a heat medium feed tube 8a to be introduced into the shell 2.

The temperature of the heat medium Hm introduced into the shell 2 iscontrolled by adjusting the temperature or quantity of flow of the heatmedium flowing from the heat medium feed tube 8 a. In addition, thetemperature of the heat medium Hm is measured with a thermometer 14inserted into the side of the inlet of the ring-shaped tube 3 a.

An inner body plate of each of the ring-shaped tube 3 a and aring-shaped tube 3 b is equipped with a flow-rectifying plate (notshown) in order to minimize the flow rate distribution of the heatmedium in a circumferential direction. A porous plate or a plate withslits is used for the flow-rectifying plate. The flow-rectifying plateis arranged in such a manner that the same quantity of flow of the heatmedium Hm is introduced into the shell 2 at the same flow rate from theentire circumference by changing an opening area of the porous plate orby changing slit intervals.

In addition, the temperature inside the ring-shaped tube 3 a, preferablythe temperature inside each of the ring-shaped tubes 3 a and 3 b, can bemonitored with a plurality of thermometers 15 arranged at even intervalalong the circumference as shown in FIG. 4. 1 to 5 baffles are typicallyequipped inside the shell 2. In FIG. 1, 3 baffles (6 a, 6 b, and 6 a)are equipped inside the shell 2. The presence of those baffles causesthe flow of the heat medium Hm in the shell 2 to center on the centralportion from the outer peripheral portion of the shell 2, to flow upwardthrough an opening of the baffle 6 a toward the outer peripheral portionwhile changing its direction, and then to reach the inner wall of theshell 2.

Then, the heat medium Hm changes its direction again to converge to thecentral portion while flowing upward through a gap between the innerwall of the shell 2 and the outer periphery of the baffle 6 b. Finally,the heat medium Hm flows upward through an opening of the baffle 6 atoward the outer periphery along the bottom face of the upper tube plate5 a in the shell 2 to be introduced into the ring-shaped tube 3 b. Afterthat, the heat medium Hm is sucked in the circulating pump 7 to becirculated in the shell 2 again.

The specific structure of a baffle used in the present invention may beany one of a segment-type noncircular baffle shown in FIG. 2 and adisc-type baffle shown in FIG. 3.

Both types of baffles have the same relationship between the flowdirection of a heat medium and the axis of a reaction tube.

The baffle 6 a has its outer periphery on the inner wall of the shell 2and has an opening around its center. In addition, the outer peripheryof the baffle 6 b is smaller than the circumference of the inner wall ofthe shell 2 so that a gap is formed between the outer periphery of thebaffle 6 b and the inner wall of the shell 2.

The heat medium changes its direction at each opening and gap whilemoving upward, and the flow rate is changed.

Thermometers 11 are equipped inside the reaction tubes 1 a, 1 b, and 1c, which are equipped inside in the shell 2. Signals are transmittedfrom thermometers to the outside of the shell 2 to measure thetemperature distribution of a catalyst layer packed inside a reactiontube in an axial direction of the reaction tube.

A plurality of thermometers 11 are inserted into the reaction tubes 1 a,1 b, and 1 c to measure temperatures at 2 to 20 points in an axialdirection.

The reaction tubes 1 a, 1 b, and 1 c equipped inside the shell 2 aredivided by the 3 baffles 6 a, 6 b, and 6 c, and are classified into 3types depending on the relationship with the flow direction of the heatmedium Hm.

That is, the reaction tube la is connected to the baffle 6 b. Therefore,the flow direction of the heat medium Hm is restrained only by thebaffle 6 b. In addition, the flow direction is not restrained by theother two baffles 6 a because the reaction tube 1 a penetrates throughopening portions of the two baffles 6 a.

The direction of the heat medium Hm introduced into the shell 2 throughthe ring-shaped tube 3 a is changed as indicated by an arrow shown inFIG. 1 at the central portion of the shell 2. Furthermore, the reactiontube 1 a is located at the position where the direction is changed, andthus the heat medium Hm that flows along the outer periphery of thereaction tube la mainly flows in parallel with the axis of the reactiontube 1 a.

The reaction tube 1 b is connected to the 3 baffles 6 a, 6 b, and 6 a sothat the flow direction of the heat medium Hm is restrained by each ofthe baffles. In addition, the heat medium Hm flowing along the outerperiphery of the reaction tube 1 b flows at a right angle with the axisof the reaction tube 1 b at nearly all positions of the reaction tube 1b. It should be noted that most of the reaction tubes equipped insidethe shell 2 are located at the position of the reaction tube 1 b.

In addition, the reaction tube 1 c is not connected to the baffle 6 band penetrates through a gap between the outer periphery of the baffle 6b and the inner wall of the shell 2. Therefore, the flow of the heatmedium Hm is not restrained by the baffle 6 b at this position and isparallel with the axis of the reaction tube 1 c.

FIG. 4 shows the positional relationship among the reaction tubes 1 a, 1b, and 1 c and the baffles 6 a, 6 b, and 6 a, and the correlation of theflow of the heat medium Hm.

When an opening portion (the most inner circle indicated by brokenlines) of the baffle 6 a is located at a converging position of the heatmedium Hm, that is, the center of the shell 2, the flow of the heatmedium Hm is parallel with-the reaction tube 1 a. Moreover, nearly noheat medium Hm flows particularly at the center of the opening portionof the baffle 6 a, and the flow rate is close to zero. In other words,heat transfer efficiency is extremely poor. Therefore, the reaction tube1 a is not provided at this position in some cases.

FIG. 5 shows another-example of the present invention in which the shell2 of the reactor is divided by an intermediate tube plate 9.

Different heating media Hm1 and Hm2 are circulated in spaces obtained bydividing the shell 2 and the temperatures of the media are separatelycontrolled.

A raw material gas Rg is introduced through a raw material gas inlet 4 aof the shell and is successively reacted to yield a product.

Heat media having different temperatures are present in the shell, andhence how each of the reaction tubes 1 a, 1 b, and 1 c is packed with acatalyst is as follows. In a case (i), each reaction tube is entirelypacked with the same catalyst and the temperature of the catalyst ischanged at the inlet and outlet of the shell to allow a reaction. In acase (ii), a catalyst is packed at the inlet portion. For rapidlycooling a reaction product, no catalyst is packed at the outlet portion,that is, the outlet portion serves as a cavity or is packed with aninert substance without reaction activity. In a case (iii), differentcatalysts are packed at the inlet and outlet portions. For rapidlycooling a reaction product, no catalyst is packed at an intermediateportion or is packed with an inert substance without reaction activity.

For example, when propylene or isobutylene is introduced as a mixed gaswith a molecular oxygen-containing gas, propylene or isobutylene isconverted into (meth)acrolein at an upper portion and is oxidized to(meth)acrylic acid at a lower portion.

Different catalysts are packed in upper and lower portions in each ofthe reaction tubes 1 a, 1 b, and 1 c, and the temperatures of thecatalysts are controlled to respective optimum temperatures, to therebycarry out a reaction. An inert substance layer that is not involved inthe reaction may be present as a partition between the upper portion andthe lower portion. In the case, the inert substance layer is provided ina portion corresponding to the position at which the outer periphery ofeach of the reaction tubes 1 a, 1 b, and 1 c is connected to theintermediate tube plate 9.

In FIG. 6, reference numeral 9 represents an intermediate tube plate,and 3 thermal shields 10 are fixed at the bottom face of theintermediate tube plate 9 by spacer rods 13.

As shown in the figure, 2 to 3 thermal shields 10 are provided within100 mm below or above the intermediate tube plate 9, whereby preferablyforming a flowless stagnant space 12 filled with the heat medium Hm1 orHm2, to provide a heat insulation effect.

Thermal shields 10 are attached to the intermediate tube plate 9 for thefollowing reason. That is, in FIG. 5, when the difference in controlledtemperature between the heat medium Hm1 introduced into the lowerportion of the shell 2 and the heat medium Hm2 introduced into the upperportion of the shell 2 exceeds 100° C., heat transfer from thehigh-temperature heat medium to the low-temperature heat medium cannotbe neglected. Thus, the precision in controlling the reactiontemperature of a catalyst may degrade at lower temperatures. In such acase, heat insulation is necessary to prevent heat transfer above and/orbelow the intermediate tube plate 9.

Here, the types and ratios of raw material gas components and theimportance of uniform packing of a catalyst will be described.

Introduced into a multitube reactor for use in vapor phase catalyticoxidation is a mixed gas of propylene or isobutylene and/or(meth)acrolein with a molecular oxygen-containing gas or with watervapor as a raw material gas Rg for a reaction.

The concentration of propylene or isobutylene ranges from 3 to 10 vol %.A molar ratio of oxygen to propylene or to isobutylene ranges from 1.5to 2.5, and a molar ratio of water vapor to propylene or to isobutyleneranges from 0.8 to 2.0.

The introduced raw material gas Rg is distributed to the reaction tubes1 a, 1 b, and 1 c and then flows through each reaction tube to react byan oxidation catalyst packed inside each reaction tube. However, thedistribution of the raw material gas Rg to each reaction tube isaffected by the packing weight, packing density, and the like of acatalyst in a reaction tube. The packing weight, packing density, andthe like are set at the time of packing a catalyst into a reaction tube.Therefore, it is essential to uniformly pack a catalyst into eachreaction tube.

To uniformize the weight of a catalyst packed inside each reaction tube,it is important to set a rigorous tolerance of a reaction tube intowhich a catalyst is packed.

The raw material gas Rg flowing through each of the reaction tubes 1 a,1 b, and 1 c is initially heated to a reaction starting temperaturewhile flowing through the inert substance layer packed at the inletportion.

The raw material (propylene or isobutylene) is oxidized by the catalystpacked as the successive layer in the reaction tube, and the temperatureof the raw material further increases by heat of reaction.

The reaction weight in the inlet portion of the catalyst layer is most.The heat of reaction generated increases the temperature of the rawmaterial gas Rg when the heat of reaction is greater than the quantityof heat removal by the heat medium Hm. In such a case, hot spots may beformed. The hot spots are often formed at a position 300 to 1,000 mmfrom the inlet of each of the reaction tubes 1 a, 1 b, and 1 c.

Here, the effect of the heat of reaction generated on a catalyst, thetemperature of a heat medium and the allowable maximum temperature ofhot spots when producing acrolein through an oxidation reaction ofpropylene with a molecular oxygen-containing gas, the type of heatmedium used, and the effect of a fluid state of the heat medium on theheat removal efficiency of the heat medium will be described.

When the heat of reaction generated exceeds the heat removal capacity ofthe heat medium Hm on the outer periphery of the corresponding reactiontube, the temperature of the raw material gas Rg further increases, andthe heat of reaction also increases. Finally, the reaction becomes outof control. In this case, the temperature of the catalyst exceeds theallowable maximum temperature, so that the catalyst undergoes aqualitative change. This change may be a main cause for thedeterionation or breakage of the catalyst.

A description is given by taking as an example a former stage reactor(for instance, the portion of the reactor above the intermediate tubeplate 9 in FIG. 5) in which acrolein is produced through an oxidationreaction of propylene with a molecular oxygen-containing gas. In thisexample, the temperature of the heat medium Hm is in the range of 250 to350° C. and the allowable maximum temperature of the hot spots is in therange of 400 to 500° C.

In addition, the temperature of the heat medium Hm in a latter stagereactor (for instance, the portion of the reactor below the intermediatetube plate 9 in FIG. 5) in which acrolein is oxidized by a molecularoxygen-containing gas to yield acrylic acid is in the range of 200 to300° C. and the allowable maximum temperature of the hot spots is in therange of 300 to 400° C.

Niter, a mixture of nitrates, is often used as the heat medium Hm thatflows inside the shell 2 surrounding the reaction tubes 1 a, 1 b, and 1c. However, a phenyl ether heat medium of an organic liquid system mayalso be used.

The heat medium Hm flows to remove heat from the outer periphery of eachof the reaction tubes 1 a, 1 b, and 1 c. However, the heat medium Hmintroduced into the shell 2 through the ring-shaped tube 3 a for heatmedium introduction flows toward the central portion from the outerperipheral portion of the shell 2 at a position and reverses its flowdirection at another position. Heat removal effects at the positionswere found to extremely differ from each other.

A heat transfer coefficient of the heat medium when the flow directionof the heat medium Hm is at a right angle with the axis of a reactiontube is in the range of 1,000 to 2,000 W/m²° C. When the flow directionis not at a right angle with the axis of a reaction tube, the heattransfer coefficient varies depending on the flow rate and on whetherthe flow is an upflow or a downflow. However, the heat transfercoefficient often falls within a narrow range of 100 to 300 W/m²° C.when niter is used as the heat medium.

On the other hand, the heat transfer coefficient of a catalyst layer ineach of the reaction tubes 1 a, 1 b, and 1 c naturally dependents on theflow rate of the raw material gas Rg, but is about 100 W/m²° C. As amatter of course, the rate determining factor of heat transfer is a gasphase in a tube as usual.

Specifically, heat transfer resistance on the outer periphery of each ofthe reaction tubes 1 a, 1 b, and 1 c when the flow of the heat medium Hmis at a right angle with the axis of the tube is 1/10 to 1/20 that ofthe gas Rg in the tube. Therefore, a change in flow rate of the heatmedium Hm hardly affects the overall heat transfer resistance.

However, when niter flows in parallel with the axis of a tube, the heattransfer coefficient in each of the reaction tubes 1 a, 1 b, and 1 c iscomparable to that outside the reaction tubes 1 a, 1 b, and 1 c.Therefore, the effect of the fluid state at the outer periphery of thetube on the heat removal efficiency is large. That is, when the heattransfer resistance at the outer periphery of a tube is 100 W/m²° C.,the overall heat transfer coefficient becomes half. Furthermore, halfthe change in heat transfer resistance at the outer periphery of thetube affects the overall heat transfer coefficient.

In each of FIGS. 1 and 5, the flow direction of the heat medium Hm inthe shell 2 is represented as an upflow by arrows. However, the presentinvention can also be applied to the opposite flow direction.

In determining the direction of a circulation flow of the heat mediumHm, a phenomenon of engulfing, in the heat medium flow, a gas that maybe present at top ends of the shell 2 and the circulating pump 7, inparticular an inert gas such as nitrogen, must be prevented.

In the case where the heat medium Hm is an upflow as shown in FIG. 1, acavitation phenomenon occurs in the circulating pump 7 when a gas isengulfed at an upper portion of the circulating pump 7. In the worstcase, the pump may break.

In the case where the heat medium Hm is a downflow, a gas engulfingphenomenon occurs also at an upper portion of the shell 2. In this case,a stagnant portion of a gas phase is formed at an upper portion of theshell 2, and an upper portion of a reaction tube corresponding to thegas stagnant portion is not cooled by the heat medium Hm.

Prevention of gas stagnation must include: providing a degas line; andreplacing a gas of the gas phase with the heat medium Hm. To achievethis, the pressure of the heat medium in the heat medium feed tube 8 ais increased and the heat medium discharging tube 8 b is provided at thehighest position as possible to increase the pressure in the shell 2.The heat medium discharging tube 8 b is provided at least above theupper tube plate 5 a.

The raw material gas Rg can be an upflow or a downflow in the reactiontubes 1 a, 1 b, and 1 c. However, the raw material gas Rg preferably ina countercurrent in relation to the heat medium flow.

Examples of a method of adjusting activity of a catalyst layer include:a method of adjusting catalyst compositions to use catalysts havingdifferent activities; and a method of adjusting activity by mixingcatalyst particles with inert substance particles to dilute thecatalyst.

A catalyst layer having a small ratio of the catalyst particles ispacked into an inlet portion of each of the reaction tubes 1 a, 1 b, and1 c. A catalyst layer having a large ratio of the catalyst particles orcatalyst layer not diluted is packed into a portion of the reactiontube, the portion located downstream with respect to the flow directionof the raw material gas. Although the degree of dilution varies by acatalyst, a (catalyst particles/inert substance particles) mixing ratiois preferably in the range of 7/3 to 3/7 in the former stage and in therange of 10/0 to 5/5 in the latter stage. 2 to 3 stages are typicallyadopted for the activity change or dilution of a catalyst.

Dilution ratios of the catalysts packed inside the reaction tubes 1 a, 1b, and 1 c do not need to be the same with each other. For example, thereaction tube 1 a has a high maximum temperature so that there is a highpossibility of catalyst deterioration. To prevent the deterioration, itis possible to lower the catalyst particle ratio in the former stage andto increase the catalyst particle ratio in the latter stage.

Differences in reaction conversions among the respective reaction tubesmay affect the average conversion and yield of the entire reactor.Therefore, it is preferable that the dilution rate is set so that thesame conversion is obtained in the respective reaction tubes even whendilution ratios are changed.

The present invention is suitably applied to a multitube reactor foroxidizing propylene or isobutylene with a molecular oxygen-containinggas or to a multitube reactor in which (meth)acrolein is oxidized with amolecular oxygen-containing gas to yield (meth)acrylic acid. A catalystused in oxidation of propylene is preferably a multicomponent mixedmetal oxide, mainly an Mo—Bi mixed metal oxide. A catalyst used inoxidation of acrolein to yield acrylic acid is preferably an Sb—Mo mixedoxide.

Propylene or isobutylene is typically oxidized in 2 stages and hencedifferent catalysts may be packed inside 2 multitube reactors to carryout a reaction. Alternatively, the present invention can also be appliedto the case of yielding (meth)acrylic acid in a single reactor with theshell of the reactor divided into 2 or more chambers by intermediatetube plates as shown in FIG. 5 and with the chambers packed withdifferent catalysts.

In a multitube reactor for oxidizing propylene or isobutylene with amolecular oxygen-containing gas, when the reactor shown in FIG. 1 isadopted and the raw material gas Rg enters from 4 a and is dischargedfrom 4 b, the concentration of the target product (meth) acrolein ishigh in the vicinity of the shell outlet 5 b. In addition, thetemperature of the raw material gas increases because the raw materialgas is heated by the heat of reaction. Therefore, in this case, a heatexchanger is additionally provided in the course of the raw material gasRg following 4 b of the shell shown in FIG. 1, to thereby sufficientlycool the reaction gas to prevent (meth)acrolein from causing anautooxidation reaction.

In the case where the reactor shown in FIG. 5 is adopted, when the rawmaterial gas Rg enters from 4 a and is discharged from 4 b, theconcentration of the target product (meth)acrolein is high in thevicinity of the catalyst layer outlet 9 in the former stage. Inaddition, the temperature of a fuel gas increases because the gas isheated by the heat of reaction.

When a catalyst is packed only into 5 a-6 a-6 b-6 a-9, no reaction iscarried out in the catalyst layer outlet portion (between 9 and 5 b) inthe latter stage of the reaction tubes 1 a, 1 b, and 1 c. The rawmaterial gas is cooled by the heat media Hm1 and Hm2 flowing throughflow paths to the shell in order to prevent (meth)acrolein from causingan autooxidation reaction. In this case, the gas outlet portion (between9 and 5 b) of each of the reaction tubes 1 a, 1 b, and 1 c is packedwith no catalyst or with an inert substance without reaction activity.However, the latter is preferably packed for improving heat transfercharacteristics.

In addition, in FIG. 5, in the case where the catalyst layer (5 a-6 a-6b-6 a-9) in the former stage on the inlet side of the raw material gasRg and the catalyst layer (9-6 a′-6 b′-6 a′-5 b) in the latter stage onthe outlet side of the gas are packed with different catalysts to obtain(meth)acrolein and (meth)acrylic acid from propylene and isobutylene,the temperature of the catalyst layer in the former stage is higher thanthat of the catalyst layer in the latter stage. Therefore, no reactionis carried out around the catalyst layer outlet (6 a-9) in the formerstage and the catalyst layer inlet (9-6 a′) in the latter stage becausea position around them has a high temperature. The raw material gas iscooled by the heat medium flowing through a flow path to the shell sidein order to prevent (meth)acrolein from causing an autooxidationreaction.

In this case, a portion into which no catalyst is packed is providedamong 6 a-9-6 a′ of the reaction tubes 1 a, 1 b, and 1 c to serve as acavity. Alternatively, an inert substance without reaction activity ispacked among 6 a-9-6 a′ of the reaction tubes 1 a, 1 b, and 1 c.However, the latter is preferably packed for improving heat transfercharacteristics.

A vapor phase catalytic oxidation reaction involves: mixing propylene orisobutylene as a raw material with molecular oxygen and an inert gassuch as nitrogen, carbon dioxide, or water vapor to prepare a rawmaterial gas; and reacting the raw material gas in the presence of asolid catalyst to yield acrolein and acrylic acid or methacrolein andmethacrylic acid. Any conventionally known catalyst is available for thecatalyst. According to the present invention, it is also possible toyield acrylic acid by subjecting propane to vapor phase oxidation byusing a Mo—V—Te mixed oxide catalyst, Mo—V—Sb mixed oxide catalyst, orthe like.

The composition of a former stage reaction catalyst (for a reactionconverting an olefin into an unsaturated aldehyde or an unsaturatedacid) that can be preferably used in the present invention isrepresented by the following general formula (I).Mo_(a)W_(b)Bi_(c)Fe_(d)A_(e)B_(f)C_(g)D_(h)E_(i)O_(j)   (I)(wherein, Mo represents molybdenum; W represents tungsten; Bi representsbismuth; Fe represents iron; A represents at least one type of elementchosen from nickel and cobalt; B represents at least one type of elementselected from the group consisting of sodium, potassium, rubidium,cesium, and thallium; C represents at least one type of element selectedfrom alkaline earth metals; D represents at least one type of elementselected from the group consisting of phosphorus, tellurium, antimony,tin, cerium, lead, niobium, manganese, arsenic, boron, and zinc; Erepresents at least one type of element selected from the groupconsisting of silicon, aluminum, titanium, and zirconium; o representsoxygen; a, b, c, d, e, f, g, h, i, and j represent atomic ratios of Mo,W, Bi, Fe, A, B, C, D, E, and O respectively; and if a=12, 0≦b≦10,0<c≦10, 0<d≦10, 2≦e≦15, 0<f≦10, 0≦g≦10, 0≦h≦4, and 0≦i≦30; and j is avalue determined from oxidation states of the respective elements.)

In the multitube reactor of the present invention, c, d, and f in theabove general formula (I) preferably satisfy 0.1≦c≦10, 0.1≦d≦10, and0.001≦f≦10.

Further, the composition of a latter stage reaction catalyst (for areaction converting an olefin into an unsaturated aldehyde or anunsaturated acid) that can be preferably used in the present inventionis represented by the following general formula (II).Sb_(k)Mo_(l)(V/Nb)_(m)X_(n)Y_(p)Si_(q)O_(r)   (II)(wherein, Sb represents antimony; Mo represents molybdenum; V representsvanadium; Nb represents niobium; X represents at least one type ofelement selected from the group consisting of iron (Fe), cobalt (Co),nickel (Ni), and bismuth (Bi) ; Y represents at least one type ofelement chosen from copper (Cu) and/or tungsten (W); Si representssilicon; O represents oxygen; (V/Nb) represents V and/or Nb; k, l, m, n,p, q, and r represent atomic ratios of Sb, Mo, (V/Nb), X, Y, Si, and Orespectively; and 1≦k≦100, 1≦l≦100, 0.1≦m≦50, 1≦n≦100, 0.1≦p≦50,1≦q≦100; and r is a value determined from oxidation states of therespective elements.) In the multitube reactor of the present invention,k, l, m, n, p, and q in the above general formula (II) preferablysatisfy 10≦k≦100, 1≦l≦50, 1<m≦20, 10≦n≦100, 1≦p≦20, and 10≦q≦100.

The shape of and molding method for a catalyst used are described. Acatalyst used in the multitube reactor of the present invention may be amolded catalyst molded through extrusion molding or tablet compressionor may be a catalyst prepared by supporting a mixed oxide composed of acatalyst component on an inert support such as silicon carbide, alumina,zirconium oxide, or titanium oxide.

The shape of a catalyst used in the present invention is notparticularly limited and may be spherical, cylindrical, ring-shaped,amorphous, or the like.

In particular, the use of a ring-shaped catalyst has an effect ofpreventing heat storage in hot spot portions.

A catalyst packed into a reaction tube inlet may have the same ordifferent composition and shape with a catalyst packed into an upperportion of the reaction tube.

An inert substance used for catalyst dilution in the present reaction isnot limited as long as the inert substance is stable under theconditions of the present reaction and has no reactivity with a rawmaterial substance and a product. Specific examples of the inertsubstance include those typically used as catalyst supports such asalumina, silicon carbide, silica, zirconium oxide, and titanium oxide.In addition, as in the case of the catalyst, the shape of the inertsubstance is not limited and may be spherical, cylindrical, ring-shaped,amorphous, or the like. The size of the inert substance may be set inconsideration of the diameter of a reaction tube and differentialpressure in a reaction tube.

In the case where a multitube reactor is used and a plurality ofreaction zones are provided by dividing the inside of each reaction tubein its axial direction, the number of reaction zones may beappropriately selected in such a manner providing the maximum effect ofthe reaction zones. However, an excessively large number of reactionzones requires much effort for catalyst packing. Therefore, anindustrially desirable number of reaction zones is about 2 to 5.

In addition, the length of a reaction zone may be appropriately selectedin such a manner that the maximum effect of the present invention isexerted because the most suitable value of the length is determined bythe catalyst type, the number of reaction zones, the reactionconditions, and the like. The length of each reaction zone is typically10 to 80%, preferably 20 to 70%, of the total length.

According to the present invention, the catalytic activity of a catalystpacked into a plurality of reaction zones is controlled by alteringmixing with an inert substance, a shape of the catalyst, a compositionof the catalyst, and a burning temperature upon catalyst preparation,and, if the catalyst is a supported catalyst, the amount of a catalystactive ingredient supported.

<First Vapor Phase Catalytic Oxidation Method>

The inventors of the present invention have devoted themselves toresearch and have confirmed that the above-mentioned problems such asyield reduction and reduced catalyst life arise when catalyst layer peaktemperature sites, which are high temperature portions of the catalystlayers, are located at portions where a heat medium does not flow at allor hardly flows due to baffles. The inventors of the present inventionhave found out that the following methods can provide a vapor phasecatalytic oxidation method solving the above-mentioned problems and havecompleted the present invention.

That is, the first vapor phase catalytic oxidation method is a vaporphase catalytic oxidation method: using a fixed bed multitubeheat-exchanger type reactor having a plurality of reaction tubes andbaffles for changing a flow path of a heat medium; circulating the heatmedium through the outside of the of the reaction tubes; and feeding araw material gas into the reaction tubes packed with a catalyst, tothereby obtain a reaction product gas, wherein the method comprises,catalyst packing specifications in the reaction tubes are determined sothat catalyst layer peak temperature sites of the reaction tubes are notlocated at the connecting sites between the baffles and the reactiontubes.

Hereinafter, the first vapor phase catalytic oxidation method will bedescribed in detail.

The first vapor phase catalytic oxidation method involves vapor phasecatalytic oxidation using a fixed bed multitube heat-exchanger typereactor having a plurality of reaction tubes and baffles for changing aflow path of a heat medium. That is,.a reaction product gas is formed inthe reactor by circulating the heat medium through the outside of thereaction tubes, and feeding a raw material gas into the reaction tubespacked with a catalyst.

In the first vapor phase catalytic oxidation method, the heat medium ispreferably used for absorbing heat of reaction generated from thereaction tubes. Any material can be used for the heat medium as long asthe material has a function of absorbing the heat of reaction generatedfrom the reaction tubes. Examples of the heat medium include: organicheating media such as partially-hydrogenated triphenyl; and inorganicmolten salts such as alkali metal (such as sodium and potassium) nitrateor nitrite, so-called niter.

Further, in the first vapor phase catalytic oxidation method, the rawmaterial gas or the catalyst for the reaction can be appropriatelyselected in accordance with a desired type of the reaction product gas.

Through the first vapor phase catalytic oxidation reaction method,(meth) acrolein or (meth) acrylic acid can be produced from propane,propylene, or isobutylene in the presence of a mixed oxide catalystusing molecular oxygen or a molecular oxygen-containing gas, forexample. To be specific, (meth)acrylic acid can be produced by:oxidizing propylene or isobutylene in the presence of a Mo—Bi mixedoxide catalyst to mainly produce (meth)acrolein (former stage reaction);and oxidizing the (meth) acrolein produced in the former stage reactionin the presence of a Mo—V mixed oxide catalyst. Further, acrylic acidcan also be produced through vapor phase oxidation of propane using aMo—V—Te mixed oxide catalyst or a Mo—V—Sb mixed oxide catalyst.

The following production systems are effective especially forcommercialization in production of the (meth)acrolein or (meth)acrylicacid through the first vapor phase catalytic oxidation method.Hereinafter, the production systems will be described using propylene asan example.

1) One-Pass System

The one-pass system involves: mixing and feeding propylene, air, andsteam to mainly produce acrolein and acrylic acid (former stagereaction); feeding the gas obtained in the former stage reaction to alatter stage reaction without separating products; and feeding air andsteam required for the latter stage reaction in addition to the gasobtained in the former stage reaction.

2) Unreacted Propylene Recycle System

The unreacted propylene recycle system for recycling a part of theunreacted propylene involves: guiding a reaction product gas containingacrylic acid obtained through the latter stage reaction to an acrylicacid collecting device; collecting the acrylic acid in an aqueoussolution; separating a part of a waste gas containing the unreactedpropylene from the collecting device; and feeding the waste gas to theformer stage reaction again.

3) Combustion Waste Gas Recycle System

The combustion waste gas recycle system involves: guiding the reactionproduct gas containing acrylic acid obtained through the latter stagereaction to the acrylic acid collecting device; collecting the acrylicacid in an aqueous solution; catalytically combusting and oxidizing allwaste gas from the collecting device to convert the unreacted propyleneor the like in the waste gas to mainly carbon dioxide and water; andfeeding a part of the obtained combustion waste gas to the former stagereaction again.

The first vapor phase catalytic oxidation method can be carried outusing any one of the above-mentioned systems for commercial production,and the production system is not particularly limited.

Further, a Mo—Bi mixed oxide catalyst represented by the general formula(I) is preferably used in the above-mentioned multitube reactor of thepresent invention as a catalyst used in the former stage reaction forobtaining the above-mentioned olefin from unsaturated aldehyde orunsaturated acid.

Further, a Mo—V mixed oxide catalyst represented by the general formulais preferably used as a catalyst used in the latter stage reaction forobtaining the above-mentioned olefin from unsaturated aldehyde orunsaturated acid.Mo_(a)V_(b)W_(c)Cu_(d)X_(e)Y_(f)O_(g)(wherein, Mo represents molybdenum; V represents vanadium; W representstungsten; Cu represents copper; X represents at least one type ofelement selected from the group consisting of Mg, Ca, Sr, and Ba; Yrepresents at least one type of element selected from the groupconsisting of Ti, Zr, Ce, Cr, Mn, Fe, Co, Ni, Zn, Nb, Sn, Sb, Pb, andBi; O represents oxygen; a, b, c, d, e, f, and g represent atomic ratiosof Mo, V, W, Cu, X, Y, and O respectively; if a=12, 2≦b≦14, 0≦c≦12,0<d≦6, 0≦e≦3, and 0≦f≦3; and g is a value determined from oxidationstates of the respective elements.)

The reaction tubes used in the first vapor phase catalytic oxidationmethod are packed with the catalyst and an inert substance for dilutionof the catalyst (hereinafter, may be referred to as “diluent”) as theneed arises.

Further, packing specifications for packing the catalyst in the reactiontubes may be set by considering all the factors involved such as a typeof the catalyst, an amount of the catalyst, a form of the catalyst(shape, size), a method for diluting the catalyst (a type of thediluent, an amount of the diluent), and lengths of reaction zones. Thelengths of reaction zones are adjusted depending on a form of thecatalyst, an amount of the catalyst, and usage of the diluent with.

The form of the catalyst and a method for molding the catalyst employedin the present invention are determined in the same manner as for theabove-mentioned multitube reactor of the present invention. Further, thediluent is determined in the same manner as for the inert substance thatemployed for the above-mentioned multitube reactor of the presentinvention.

A mixing ratio of the catalyst and the diluent is not particularlylimited, but when the mixing ratio is extremely large or small, themixing ratio may be adjusted so that the catalyst and the diluent areuniformly mixed.

Further, the packing specifications for packing the catalyst may differaccording to layers of reaction zones of one reaction tube. For example,packing specifications for packing the catalyst packed in an upperportion of a reaction tube may differ from the packing specificationsfor packing the catalyst packed in a lower portion of the reaction tube.Generally, the preferred number of the reaction zones is up to 2 to 3 inone reaction tube.

Further, the catalyst is preferably packed so that the catalyticactivity increases from an inlet portion of the reaction tubes where araw material gas is introduced toward an outlet portion of the reactiontubes.

In the first vapor phase catalytic oxidation method, catalyst layer peaktemperature sites of the reaction tubes are not located at connectingsites between the baffles and the reaction tubes.

Here, the catalyst layer peak temperature refers to the highesttemperature of the catalyst layer measured during a reaction. Thecatalyst layer peak temperature sites refer to: a portion of thecatalyst layer having the highest temperature when the catalyst ispacked in a reaction tube in a single layer; and to respective portionsof the catalyst layers having the highest temperature in respectivereaction zones when the catalyst is packed in several reaction zones.

The catalyst layer peak temperature is determined as follows.

The temperatures of the respective portions of the catalyst layer aredetermined by packing the catalyst after inserting a multi-pointthermocouple to the reaction tube and measuring the temperatures of therespective portions of the catalyst layer. Note that, the number ofmeasurement points of the multi-point thermocouple is generally 5 to 100points, preferably 7 to 50 points, and more preferably 10 to 30 points.Alternatively, the temperature is determined by packing the catalystafter inserting a well in the reaction tubes and measuring thetemperature while moving thermocouple inside the well. The catalystlayer peak temperature indicates portions of the catalyst layer havingthe highest temperatures in the respective reaction zones when using amovable thermocouple and portions of measurement points having thehighest temperatures in the respective reaction zones when using themulti-point thermocouple.

In the first vapor phase catalytic oxidation method, the connectingsites between the baffles and the reaction tubes, more specifically,refer to sites where the baffles and the reaction tubes are fixed toeach other through welding, a frange, or the like or where the bafflesexist across the reaction tubes if they are not fixed to each other.

Further, in the first vapor phase catalytic oxidation method, thecatalyst packing specifications in the reaction tubes are set so thatthe catalyst layer peak temperature sites of the reaction tubes are notlocated at the connecting sites between the baffles and the reactiontubes That is, the packing specifications are changed for the reactiontubes having the catalyst layer peak temperature sites of the reactiontubes located at the connecting sites between the baffles and thereaction tubes. The catalyst packing specifications can be changed inview of the respective factors such as a type of the catalyst, an amountof the catalyst, a form of the catalyst (shape, size), a method fordiluting the catalyst (a type of the diluent, an amount of the diluent),and lengths of reaction zones.

In the first vapor phase catalytic oxidation method, the catalyst ispreferably packed so that the catalyst layer peak temperature sitesinside the reaction tubes are not located in the range of ±100% ofbaffle thickness from the center of the thickness of a baffle, where thedirection along a surface of one side of the baffle is referred to asa + direction and the direction along a surface of the other side of thebaffle is referred to as a − direction to the center of the tickness ofthe baffle. Here, the thickness of the baffles generally used is about 5to 50 mm.

In the first vapor phase catalytic oxidation method, the catalystpacking specifications are more preferably changed by providing in onereaction tube at least two catalyst layers with different catalystpacking specifications. The catalyst layer peak temperature sites can betransferred longitudinally along the reaction tube by particularlychanging the lengths of the reaction zones for the reaction tube havinga plurality of reaction zones.

Further, In the first vapor phase catalytic oxidation method, thecatalyst packing specifications are preferably set to minimize the heatof reaction at the connecting sites between the baffles and the reactiontubes by, for example, forming an inert layer composed of the diluentalone or increasing an amount of the diluent at the connecting sites.

Further, in the first vapor phase catalytic oxidation method, aplurality of reaction tubes with different catalyst packingspecifications may be formed inside one reactor as long as the catalystlayer peak temperature sites of the reaction tubes are not located atthe connecting sites between the baffles and the reaction tubes.

FIG. 7 shows a first embodiment mode of a fixed bed multitubeheat-exchanger type reactor employed in the first vapor phase catalyticoxidation method.

FIG. 7 shows: a reactor 1; a raw material gas introducing port (for adownflow case) or a reaction product gas discharging port (for an upflowcase) 2; a reaction product gas discharging port (for a downflow case)or a raw material gas introducing port (for an upflow case) 3; areaction tube (catalyst packed inside) 4; an upper tube plate 5; a lowertube plate 6; baffles 7, 8, and 9; a heat medium outlet nozzle 10; aheat medium inlet nozzle 11; a heat medium inlet line for reactiontemperature adjustment 13; and a heat medium overflow line 14.

Note that the fixed bed multitube heat-exchanger type reactor shown inFIG. 7 is a structure employed when allowing the heat medium to flow inan upflow direction, but the heat medium can be obviously flown in adownflow direction as well in the first vapor phase catalytic oxidationmethod.

The raw material gas is mixed with air and/or a diluent gas, a recyclegas, or the like, introduced from the raw material gas introducing port(2 or 3) to the reactor (1), and fed to the reaction tube (4) packedwith the catalyst. The reaction product gas produced by oxidationthrough a catalytic oxidation reaction inside the reaction tube and anunreacted gas are discharged from the reaction product gas dischargingport (3 or 2).

The heat medium is introduced from the heat medium inlet nozzle (11) toa shell by a pump (12), passed through inside the shell while removingthe heat of reaction generated inside the reaction tube, discharged fromthe heat medium outlet nozzle (10), and circulated by the pump. The heatmedium temperature is controlled by introducing the heat medium from theheat medium inlet line for reaction temperature adjustment (13), and theamount of the heat medium introduced from the heat medium inlet line forreaction temperature adjustment (13) is discharged from the heat mediumoverflow line (14).

A structure of the baffles of the fixed bed multitube heat-exchangertype reactor employed in the first vapor phase catalytic oxidationmethod is not particularly limited. Any type of the fixed bed multitubeheat-exchanger type reactor can be used including: a double segment-typebaffle type shown in FIG. 8; a disc and doughnut baffle type shown inFIG. 9; and a multi baffle type shown in FIG. 10. Note that, in FIGS. 8to 10, shapes of the baffles and a flow of the heat medium aredescribed.

FIG. 11 is a schematic diagram illustrating that the heat medium doesnot flow through the connecting sites between the baffles and thereaction tubes fixed through welding, franges, or the like in the fixedbed multitube heat-exchanger type reactor. Further, FIG. 12 is aschematic diagram illustrating that the amount of the heat mediumflowing through the connecting sites between the baffles and thereaction tubes are limited if the baffles exist across the reactiontubes, if not fixed to the reaction tubes. In FIGS. 11 and 12, referencenumerals 15 and 16 represent a reaction tube and a baffle, respectively.Further, reference numerals 17 and 18 represent a flow of the heatmedium.

<Second Vapor Phase Catalytic Oxidation Method>

The inventors of the present invention have found that the process gastemperature in the vicinity of the product discharging port of thereactor can be reduced to prevent an autooxidation reaction, even underconditions of high product concentration by diluting the catalyst withthe inert substance for reducing the catalyst layer peak temperatureinside the reaction tubes and employing a countercurrent-type heatmedium circulation method, to thereby complete the present invention.

That is, the gist of the second vapor phase catalytic oxidation methodis as described below.

The second vapor phase catalytic oxidation method is a method ofobtaining (meth) acrolein and/or (meth) acrylic acid by oxidizingpropylene, propane, isobutylene, and/or (meth)acrolein through vaporphase catalytic oxidation with a molecular oxygen-containing gas using amultitube reactor having: a cylindrical shell having a raw material feedport and a product discharging port; a plurality of ring-shaped tubesarranged on an outer periphery of the cylindrical shell for introducingor discharging a heat medium into or from the cylindrical shell; acirculating device connecting the plurality of ring-shaped tubes witheach other; a plurality of reaction tubes restrained by a plurality oftube plates of the reactor and containing a catalyst; and a plurality ofbaffles arranged in a longitudinal direction of the reaction tubes forchanging a direction of the heat medium introduced into the shell,wherein the method comprises: packing a Mo—Bi catalyst and/or Sb—Mocatalyst in the reaction tubes so that activity increases from a processgas inlet to a process gas outlet of the reaction tubes; and allowingthe heat medium and the process gas to flow in a countercurrent.

Hereinafter, the second vapor phase catalytic oxidation method will bedescribed in detail.

A multitube reactor is generally used when heat of reaction is extremelylarge as in an oxidation reaction and when productivity of the reactormust be improved by protecting a catalyst through rigorous control ofcatalyst reaction temperature and maintaining high catalyst performance.

Recently, production of acrylic acid from propylene or propane, orproduction of methacrylic acid from isobutylene (hereinafter,collectively referred to as production of (meth)acrylic acid) hassignificantly increased with increasing demand. Many plants have beenconstructed worldwide, and a production scale per a plant has increasedto 100,000 tons or more per year. Increase of a production scale of aplant requires increase of production per oxidation reactor. As aresult, a load on a vapor phase catalytic oxidation reactor forpropylene or isobutylene has increased. Along with the load increase,the multitube reactor has been required to provide higher performance interms of increase in an amount of heat removal, and development of themultitube reactor has become important.

The second vapor phase catalytic oxidation is a vapor phase catalyticoxidation method comprising oxidizing an oxidizable reactant throughvapor phase catalytic oxidation with a molecular oxygen-containing gasusing a multitube reactor having: a cylindrical shell having a rawmaterial feed port and a product discharging port; a plurality ofring-shaped tubes arranged on an outer periphery of the cylindricalshell for introducing or discharging a heat medium into or from thecylindrical shell; a circulating device for connecting the plurality ofring-shaped tubes with each other; a plurality of reaction tubesrestrained by a plurality of tube plates of the reactor and containing acatalyst; and a plurality of baffles arranging in a longitudinaldirection for changing a direction of the heat medium introduced intothe shell, the method being characterized by comprising: packing a Mo—Bicatalyst and/or Sb—Mo catalyst in the reaction tubes so that activityincreases from a process gas inlet to a process gas outlet of thereaction tubes; and allowing the heat medium and the process gas to flowin a countercurrent.

In particular, the second vapor phase catalytic oxidation method is avapor phase catalytic oxidation method of obtaining (meth)acroleinand/or (meth)acrylic acid through vapor phase catalytic oxidation ofpropylene, propane, or isobutylene, and/or (meth)acrolein as anoxidizable reactant with a molecular oxygen-containing gas.

In the second vapor phase catalytic oxidation method, the term “processgas” refers to a gas involved in a vapor phase catalytic oxidationreaction including an oxidizable reactant as a raw material gas, amolecular oxygen-containing gas, and obtained products.

Hereinafter, one embodiment mode of the second vapor phase catalyticoxidation method will be descried with reference to FIG. 1. The reactiontubes 1 b and 1 c are arranged in the shell 2 of the multitube reactor,fixed onto the tube plates 5 a and 5 b. A raw material feed port as aninlet of a raw material gas or a product discharging port as an outletof the products is represented by reference numeral 4 a or 4 b. As longas the process gas and the heat medium are in a countercurrent, a flowdirection of the process gas is not limited. In FIG. 1, the flowdirection of the heat medium inside the shell is indicated by arrows asan upflow, and thus reference numeral 4 b represents the raw materialfeed port. The ring-shaped tube 3 a for introducing the heat medium isprovided on the outer periphery of the shell. The heat mediumpressurized with the circulating pump 7 of the heat medium flows upwardinside the shell from the ring-shaped tube 3 a. The flow direction ofthe heat medium is changed by plurally and alternately arranging theperforated baffle 6 a having an opening portion in the vicinity of thecenter of the shell and the perforated baffle 6 b provided to have anopening portion between the baffle and the outer periphery of the shell.The heat medium is then returned from the ring-shaped tube 3 b to thecirculating pump. A part of the heat medium absorbing the heat ofreaction flows toward the discharging tube provided in upper portion ofthe circulating pump 7, is cooled with the heat exchanger (not shown),and its introduced into the reactor again from the heat medium feed line8 a. The heat medium temperature is adjusted by adjusting temperature ora flow rate of a returning heat medium introduced from the heat mediumfeed line 8 a to control thermometer 14.

The heat medium temperature is adjusted so that a temperature differenceof the heat medium between the heat medium feed line 8 a and the heatmedium draw line 8 b is 1° C. to 10° C., preferably 2° C. to 6° C.,though depending on the performance of the catalyst used.

A flow-rectifying plate (not shown) is preferably provided in a bodyplate portion inside the ring-shaped tubes 3 a and 3 b for minimizing aflow rate distribution of the heat medium in a circumferentialdirection. A porous plate or a plate provided with slits is used as theflow-rectifying plate, and the flow of heat medium is adjusted bychanging an opening area of the porous plate or slit intervals so thatthe heat medium flows at the same flow rate from the entirecircumference. The temperature inside the ring-shaped tubes (3 a,preferably also 3 b) can be monitored by providing the plurality ofthermometers 15.

The number of the baffles provided inside the shell is not particularlylimited, but three baffles (2 baffles of 6 a type and 1 baffle of 6 btype) are preferably provided as usual. The baffles prevent an upflow ofthe heat medium, changes the flow of the heat medium to a lateraldirection with respect to an axial direction of the reaction tubes. Theheat medium converges from an outer peripheral portion to a centralportion of the shell, changes direction in the opening portion of thebaffle 6 a, flows to the outer peripheral portion of the shell, andreaches the outer cylinder of the shell. The heat medium changesdirection again on an outer periphery of the baffle 6 b, converges tothe central portion, flows upward through the opening portion of thebaffle 6 a, flows along the upper tube plate 5 a toward the outerperiphery of the shell, and flows through the ring-shaped tube 3 b tocirculate to the pump.

Thermometers 11 are inserted to the reaction tubes arranged inside thereactor and signals are transmitted to the outside of the reactor, tothereby record temperature distributions of the catalyst layers in anaxial direction of the reactor. Multiple thermometers are inserted tothe reaction tubes, and one thermometer measures temperatures of 5 to 20points in an axial direction of the tube.

The reaction tubes are classified into two types depending on theirplacements in relation to opening portions of the three baffles, thatis, on flow directions of the heat medium.

The reaction tube 1 b is restrained by the three baffles 6 a, 6 b, and 6c, and most of the reaction tubes are arranged in this region. The flowdirection of the heat medium in the entire region of the reaction tube 1b is substantially at a right angle with an axial direction of thereaction tubes. The reaction tube 1 c is in the vicinity of the outerperiphery of the shell, is not restrained by the baffle 6 b, and isprovided in the outer peripheral portion of the baffle 6 b. The centralportion of the reaction tube 1 c is in a region where a flow directionof the heat medium changes, in this region, that is, in the centralportion of the reaction tube 1 c, the heat medium flows in parallel withan axial direction of the reaction tubes.

FIG. 4 shows a view of the reactor of FIG. 1 seen from above. Not onlythe flow of the heat medium becomes parallel with the axial direction ofthe reaction tubes but also the flow rate of the heat medium becomesextremely small to provide extremely poor heat transfer efficiency inthe region where the heat medium converges at the opening portion of thebaffle 6 a, that is, at the center of the shell. Thus, the reactiontubes are not provided in the central portion of the region in thesecond vapor phase catalytic oxidation reaction.

The baffles used in the second vapor phase catalytic oxidation methodincludes: the baffle 6 a having an opening portion in the vicinity ofthe central portion of the shell; and the baffle 6 b having an openingbetween the outer peripheral portion of the baffle 6 b and the outercylinder of the shell. The heat medium changes direction at therespective opening portions, preventing a by-pass flow of the heatmedium and enabling a change in flow rate. Segment-type noncircularbaffles shown in FIG. 2 or disc-type baffles shown in FIG. 3 can beapplied as long as the baffles are arranged as described. Therelationship between the flow direction of the heat medium and the axialdirection of the reaction tubes does not change with both types ofbaffles.

The disc-type baffles are particularly used often as general baffles. Anopening area in the central portion of the baffle 6 a is preferably 5 to50%, more preferably 10 to 30% of a sectional area of the shell. Theopening area between the baffle 6 b and the shell body plate 2 ispreferably 5 to 50%, more preferably 10 to 30% of a sectional area ofthe shell. A too small opening ratio of the baffles (6 a and 6 b)provides a long flow path of the heat medium, increasing a pressure lossbetween the ring-shaped tubes (3 a and 3 b) and requiring high power forthe heat medium circulating pump 7. A too large opening ratio of thebaffles increases the number of the reaction tubes (1 c) Most of thebaffles are arranged at equal spacings (spacing between baffles 6 a and6 b, and spacing between baffle 6 a and each of tube plates 5 a and 5b), but the baffles need not to be arranged at equal spacings. It ispreferable that a required flow rate of the heat medium determined byheat of oxidation reaction generated inside the reaction tubes isensured and a pressure loss of the heat medium remains low. Hot spotpositions in a temperature distribution in the reaction tubes and thebaffle positions must not be the same from the ring-shaped tube 3 a atthe inlet of the heat medium. This is because the flow rate of the heatmedium decreases in the vicinity of baffle surface, providing a smallheat transfer coefficient. Thus, hot spot temperature further increaseswhen the baffle positions overlap the hot spot positions.

Studies are preferably conducted for preventing the hot spot positionfrom being located in the same position as the baffles, throughexperiments with small scale devices (such as bench facility and a pilotfacility) or computer simulation carried out in advance.

The types and ratios of raw material gas components and importance ofuniform packing of the catalyst are the same as those for theabove-mentioned multitube reactor of the present invention. Note that,in the second vapor phase catalytic oxidation method, concentration ofpropylene, propane, or isobutylene in the raw material gas is preferably6 to 10 mol %.

The arrangement of the catalyst in layers inside the reaction tubes,which increases the activity from the raw material gas inlet to thecutlet, can suppress hot spot formation and heat storage of the hot spotportions. Thus, the reaction can be carried out safely and efficiently,to thereby attain improvements on productivity without reducing thecatalyst life.

Various methods for changing the catalytic activity inside the reactiontubes can be applied to catalyst packing to the reaction tubes of themultitube reactor according to the second vapor phase catalyticoxidation method. Examples thereof include: a method of using catalystshaving different catalytic activities by adjusting catalystcompositions; and a method of adjusting the activities by mixingcatalyst particles with inert substance particles and diluting thecatalyst. To be specific, a catalyst having a high ratio of the inertsubstance particles and a catalyst having a low ratio of the inertsubstance particles are packed in the raw material gas inlet portion ofthe reaction tubes and the outlet portion of the reaction tubes,respectively. The ratio of the inert substance particles used differsdepending on the catalyst. The ratio of the inert substance particlesused in a first stage is often 0.3 to 0.7. The ratio of the inertsubstance particles used in a second stage is suitably 0.5 to 1.0. Twoto five stages are adopted in the change of activity and the dilution ofthe catalyst generally.

A dilution degree of the catalyst packed in the reaction tubes need notbe the same for all the reaction tubes. For example, a portion in thevicinity of the reaction tube center within the reaction tube 1 b hashigh hot spot temperature, and thus has a high possibility of catalystdeterioration. To prevent catalyst deterioration, the reaction tube insuch a portion can have a smaller ratio of the inert substance in thefirst stage compared to those of the reaction tubes in other portions,and on the other hand, can have a larger ratio of the catalyst in thesecond stage compared to those of the reaction tubes in other portions.Different reaction conversions of the respective reaction tubes affectthe average conversion or yield of the entire reactor. Thus, even whenthe dilution degree is changed, it is preferable to set the respectivereaction tubes to obtain the same conversions.

The type and shape of the inert substance used in the second vapor phasecatalytic oxidation reaction method are the same as those for theabove-mentioned multitube reactor of the present invention.

The raw material gas flowing through the reaction tubes is heated whilefirst flowing through catalyst layers packed in the raw material gasinlet portions of the reaction tubes and having a low catalyticactivity, and reaches a reaction starting temperature. The raw material(propylene or isobutylene) is oxidized through an oxidation reaction bya catalyst included in succeeding layers in the reaction tubes, and isheated to higher temperature by the heat of oxidation reaction. Thereaction weight is most in the catalyst layers in the vicinity of theraw material gas inlet. The heat of reaction generated increases thetemperature of the raw material gas when the heat of reaction is greaterthan the heat removal by the heat medium generally, thereby forming thehot spots. The hot spots, though depending on catalytic activityadjustment, often form at positions from the raw material gas inlet ofthe reaction tubes to 10 to 80% of the entire length of the reactiontubes. For example, the hot spot form at positions 0.3 to 3.2 m from theraw material gas inlet of the reaction tubes that are 3 to 4 m long.

The effect of the generated heat of reaction on the catalyst, the heatmedium temperature in acrolein production through an oxidation reactionof propylene with a molecular oxygen-containing gas, the allowablemaximum temperature of the hot spots, the type of the heat medium usedin the second vapor phase catalytic oxidation reaction, and the effectof a fluid state of the heat medium on heat removal efficiency are thesame as those of the above-mentioned multitube reactor of the presentinvention.

Inner diameters of the reaction tubes significantly affecting a gaslinear velocity are very important because: inside of the reaction tubescontaining an oxidation catalyst inside the oxidation reactor is in avapor phase; the gas linear velocity is limited by resistance of thecatalyst; and the heat transfer coefficient inside the reaction tubesare very small, the heat transfer becoming rate determining.

The inner diameters of the reaction tubes of the multitube reactoraccording to the second vapor phase catalytic oxidation reaction methoddepend on the amount of the heat of reaction and a particle size of thecatalyst inside the reaction tubes, but the inner diameter is preferably10 to 50 mm, more preferably 20 to 30 mm. Too small inner diameters-ofthe reaction tubes decrease the amount of the catalyst packed andincrease the number of reaction tubes with respect to the necessaryamount of the catalyst, thereby requiring a large reactor. On the otherhand, too large inner diameters of the reaction tubes provide a smallreaction tube surface area with respect to the necessary amount of thecatalyst, thereby reducing a heat transfer area for removal of the heatof reaction.

The second vapor phase catalytic oxidation method is suitably appliedto: a vapor phase catalytic oxidation reaction for obtaining(meth)acrolein by oxidizing propylene, propane, or isobutylene with amolecular oxygen-containing gas; and a vapor phase catalytic oxidationreaction for obtaining (meth)acrylic acid by oxidizing (meth)acroleinwith a molecular oxygen-containing gas. A Mo—Bi multi-component mixedmetal oxide is used as the catalyst for the oxidation of propylene,propane, and isobutylene, and a Sb—Mo multi-component mixed metal oxideis used as the catalyst for the oxidation of acrolein to produce acrylicacid.

Note that, the Mo—Bi catalyst preferably used in the second vapor phasecatalytic oxidation method is the same as that represented by thegeneral formula (I) in the above-mentioned multitube reactor of thepresent invention. Note that, the Mo—Bi catalyst used in the secondvapor phase catalytic oxidation method is preferably produced throughmethods disclosed in JP 06-013096 B and the like, for example. Further,the Sb—Mo catalyst is preferably produced through methods disclosed inJP 06-38918 B and the like, for example.

The Mo—Bi catalyst is produced following general production methodsexcept that a mixed carbonate salt of a C component and Bi is preparedin advance as a Bi source compound, for example. The preparation of themixed carbonate salt of a C component and B in advance involves, forexample: mixing predetermined amounts of respective aqueous nitratesolutions of Bi and the C component; adding the nitrate solutionsdropwise to an aqueous solution of ammonium carbonate or ammoniumbicarbonate while mixing the whole; and washing the obtained precipitateand drying the precipitate if necessary.

The production of the Mo—Bi catalyst generally includes an integrationstep of performing integration of source compounds of the respectiveelements in an aqueous system and a heating step. Here, the term“integration of source compounds of the respective elements in anaqueous system” means temporarily or gradually integrating aqueoussolutions or aqueous dispersions of the respective compounds. Here, theterm “source compounds of the respective elements” does not meancompounds of the respective elements alone, but includes compoundscollectively containing multiple elements (such as ammoniumphosphomolybdate for Mo and P). Further, the term “integration” does notmean integration of the source compounds of the respective elementsalone, but also includes integration with support materials such asalumina, silica-alumina, and refractory oxides, which may be used ifnecessary.

On the other hand, “heating” is carried out for the purposes including:formation of separate oxides and/or mixed oxides of the source compoundsof the respective elements; and/or formation of oxides and/or mixedcompounds of the mixed oxides obtained through integration; and/or heattreatment of the final mixed oxide products. Further, the heating neednot be applied to primarily integration products of the source compoundsof the respective elements, and the heating is not necessarily limitedto once.

Thus, in the second vapor phase catalytic oxidation method, the term“heating” includes heating the source compounds of the respectiveelements separately and gradually forming the oxides (and may includeforming mixed oxides). Further, the term “including an integration stepand a heating step” means that steps of drying, pulverization, molding,and the like may be included in addition to the two steps.

In the second vapor phase catalytic oxidation method, the Bi sourcecompound is bismuth subcarbonate which is water-insoluble and containingMg, Ca, Zn, Ce, and/or Sm. The compound is preferably used in a powderform. The compounds as raw materials for catalyst production may consistof particles larger than the powder but preferably consist of smallparticles, considering the heating step for thermal diffusion. Thus, ifthe compounds as raw materials do not consist of small particles, thecompounds are preferably pulverized before the heating step.

A specific example of the catalyst production method according to thesecond vapor phase catalytic oxidation method is as follows. Aqueoussolutions of compounds of iron, cobalt, and nickel, preferably nitratesof the respective elements are added to a suitable aqueous solution of amolybdenum compound, preferably ammonium molybdate. Further, aqueoussolutions of compounds of sodium, potassium, rubidium, thallium, boron,phosphorus, arsenic, and/or tungsten, preferably water-soluble salts ofthe respective elements are added to the mixture. Further, particulateor colloidal silica is added to the mixture if necessary. Next, bismuthsubcarbonate powder containing a C component prepared in advance isadded to the mixture. Bismuth subcarbonate containing a C component inadvance is prepared as described above by: mixing bismuth and aqueoussolutions such as Mg, Ca, Zn, Ce, and/or Sm, preferably aqueoussolutions of nitrates of the respective elements; adding the aqueoussolutions dropwise to an aqueous solution of ammonium carbonate orammonium bicarbonate while mixing the whole; and washing the obtainedslurry with water and the drying the slurry.

Next, the obtained slurry is sufficiently agitated, and then dried. Thedried downstream or cake product is subjected to heat treatment in airat 250 to 350° C. for a short period of time. Here, the obtainedheat-treated product already contains salts of iron, cobalt, and nickelwith acidic oxides, but contains bismuth subcarbonate mostly remained ina form of the raw material. This fact indicates that bismuthsubcarbonate may be added at any time.

The obtained decomposed product is shaped into an arbitrary shapethrough methods such as extrusion molding, tablet compression, andsupport molding. The shaped product is then subjected to final heattreatment preferably at 450 to 650° C. for about 1 to 16 hours.

Further, the Sb—Mo catalyst preferably used in the second vapor phasecatalytic oxidation method is the same as that represented by thegeneral formula (II) in the above-mentioned multitube reactor of thepresent invention. The Sb—Mo catalyst used in the second vapor phasecatalytic oxidation method is preferably produced using a mixed oxiderepresented by Sb—X—Si—O as a Sb source compound heated at 600 to 900°C.

Such a mixed oxide can be obtained by using: metal Sb, antimony oxide,or the like as an Sb source; nitrates, halides, or the like of the Xelements as a raw material for an X component; and colloidal silica,particulate silica, or the like as an Si source; and subjecting a solidto heat treatment in the presence of molecular oxygen (such as air) at600 to 900° C., preferably 650 to 850° C., the solid being obtained by,for example: adding the Sb source or Si source to an aqueous solution ofan X component raw material; and evaporating the mixture to drynessunder stirring.

Atomic ratios of the respective elements of the mixed oxide representedby Sbw-Xx-Siy-Oz is 1≦w≦40 (preferably 1≦w≦20), 1≦x≦20 (preferably1≦x≦10), and 1≦y≦10 (preferably 1≦y≦5). Note that, z is a valuedetermined from an oxidation degree of the respective elements.

The Sb—Mo catalyst can be produced general production methods of a mixedoxide catalyst except that such a Sb mixed oxide is used.

The above-mentioned mixed oxide preferably accounts for at least 25%,preferably 50 to 100% of a final catalyst of the Sb—Mo catalyst.

A specific example of catalyst production involves wet mixing thethus-obtained Sb—X—Si—O mixed oxide powder with: multiple acids of Mo,V, or Nb (such as molybdic acid or phosphomolybdic acid) or saltsthereof (such as ammonium salt); hydroxides or salts of those metals;and Y components (such as copper compound and tungsten compound). Theproduction method further involves concentrating and drying the mixture,and then pulverizing the dried mixture.

The method for molding the catalyst, form, and shape of the catalystused in the second vapor phase catalytic oxidation method are the sameas those for the above-mentioned multitube reactor of the presentinvention.

Note that, the catalyst packed at the raw material gas inlet of thereaction tubes may have the same composition and form as, or may havedifferent compositions and forms from, the catalyst packed at the outletof the reaction tubes.

The second vapor phase catalytic oxidation method can be applied to anyone of cases which performs a reaction employing two multitube reactorspacked with different catalysts; and a reaction employing one reactorhaving a shell divided into two or more chambers by intermediate tubeplates and having the respective chambers packed with differentcatalysts for obtaining (meth)acrylic acid at once, because(meth)acrylic acid production involves two-stage oxidation of propyleneor isobutylene.

FIG. 5 shows a multitube reactor having a shell divided by theintermediate tube plate 9, and the second vapor phase catalyticoxidation method can be also applied to a method employing the reactor.Different heat mediums circulate in the respective divided spaces, andthe spaces are controlled to different temperatures. A raw material gasmay be introduced from either the port 4 a or 4 b. In FIG. 5, a flowdirection of the heat medium inside the shell is indicated by arrows asan upflow, and thus, reference numeral 4 b represents the raw materialfeed port in which the raw material gas process gas flows in acountercurrent to the heat medium. The raw material introduced from theraw material feed port 4 b successively reacts inside the reaction tubesof the reactor.

The multitube reactor shown in FIG. 5 includes heat mediums havingdifferent temperatures in top and bottom areas (area A and area B inFIG. 5) of the reactor divided by the intermediate tube plate 9. Thecatalyst and the like inside the reaction tubes are packed in the samemanner as in the above-mentioned multitube reactor of the presentinvention.

A mixed gas containing propylene, propane, or isobutylene with amolecular oxygen-containing gas is introduced from the raw material feedport 4 b to the multitube reactor shown in FIG. 5 employed in the secondvapor phase catalytic oxidation method, for example. First, the mixedgas is converted to (meth)acrolein in a first stage (reaction tubes inarea A) for a former stage reaction, and the (meth)acrolein is thenoxidized in a second stage (reaction tubes in area B) for a latter stagereaction, to thereby produce (meth)acrylic acid. A first stage portionof the reaction tubes (hereinafter, may also be referred to as “formerstageportion”) and a second stage portion of the reaction tubes(hereinafter, may also be referred to as “latter stage portion”) arepacked with different catalysts and are controlled to differenttemperatures for a reaction under optimum conditions. The inertsubstance not involved in the reaction is preferably packed in a portionwhere the intermediate tube plate exists between the former stageportion and the latter stage portion of the reaction tubes.

FIG. 6 is an enlarged view of the intermediate tube plate and thevicinity thereof. The former stage portion and the latter stage portionare controlled to different temperatures. However, precision of reactiontemperature at lower temperatures tends to degrade when the temperaturedifference exceeds 100° C. because heat transfer from a high-temperatureheat medium to a low-temperature heat medium cannot be neglected. Insuch a case, heat insulation is required above or below the intermediatetube plate for preventing the heat transfer. FIG. 6 shows a caseemploying a heat insulation board, and two to three thermal shields 10are provided at positions of about 10 cm below or above the intermediatetube plate to form a flowless stagnant space 12 filled with the heatmedium. It is preferable to produce a heat insulation effect thereby.Thermal shields 10 are fixed to the intermediate tube plate 9 by, forexample, spacer rods 13.

The flow direction of the heat medium inside the shell is indicated byarrows as an upflow in FIGS. 1 and 5, but the second vapor phasecatalytic oxidation method can also be applied to reactors havingopposite directions of the heat medium. A direction of circulation flowof the heat medium must be set to prevent a phenomenon of engulfing, inthe heat medium, a gas, specifically, an inert gas such as nitrogenexisting on upper ends of the shell 2 and the circulating pump 7. Thegas may be engulfed in an upflow heat medium in an upper portion insidethe circulating pump 7 and a cavitation phenomenon may be caused insidethe circulating pump, possibly resulting in a worst case of pumpbreakdown. The gas may also be engulfed in a downflow heat medium in anupper portion of the shell and a stagnant portion of a gas phase mayform in an upper portion of the shell, thereby preventing cooling of theupper portion of the reaction tubes provided in the stagnant portion bythe heat medium.

Prevention of gas stagnation requires of a degas line and replacing agas in a gas phase with the heat medium. For that reason, inner pressureincrease in the shell is tried by increasing a pressure of the heatingmedium in a heat medium feed line 8 a and providing a heat medium drawline 8 b at a highest position as possible. The heat medium draw line ispreferably provided at least above a tube plate 5 a.

In a multitube reactor oxidizing propylene, propane, or isobutylene witha molecular oxygen-containing gas, when the multitube reactor shown inFIG. 1 is employed, and a process gas is downflow, that is, when the rawmaterial gas is introduced from the raw material gas inlet 4 b and theproducts are discharged from the product discharging port 4 a,concentration of the target product, (meth) acrolein, is high and theprocess gas temperature increases through heating by the heat ofreaction at the vicinity of the product discharging port 4 a of thereactor. Thus, a heat exchanger is preferably provided after the productdischarging port 4 a of the reactor shown in FIG. 1, to therebysufficiently cool the process gas and prevent an autooxidation reactionof (meth)acrolein.

Further, when the multitube reactor shown in FIG. 5 is employing, and aprocess gas is downflow, that is, when the raw material gas isintroduced from the raw material gas inlet 4 b and the products aredischarged from the product discharging port 4 a, concentration of thetarget product, (meth)acrolein, is high in the vicinity of theintermediate tube plate 9 which is an end point of the first stage(reaction tubes in area A) and the process gas temperature increasesthrough heating by the heat of reaction. If the catalyst is packed inthe first stage alone (reaction tubes in area A: 5 a-6 a-6 b-6 a-9), areaction is inhibited in the second stage of the reaction tubes 1 b and1 c (reaction tubes in area B: between 9 and 5 b) and the process gas iscooled by the heat medium flowing through a flow path to the shell, tothereby prevent an autooxidation reaction of (meth)acrolein. In thiscase, the reaction tubes 1 b and 1 c in area B (between 9 and 5 b) arenot packed with the catalyst, and the reaction tubes are left ascavities or packed with a solid without reaction activity. The latter isdesirable for improving characteristics of heat transfer.

Further, catalyst layer temperature of the first stage becomes highercompared to the catalyst layer temperature of the second stage whenpacking different catalysts in the first stage (reaction tubes in areaA: 5 a-6 a-6 b-6 a-9) and the second stage (reaction tubes in area B:9-6 a′-6 b′-6 a′-5 b) of the multitube reactor shown in FIG. 5,obtaining (meth)acrolein from propylene, propane, or isobutylene in thefirst stage, and obtaining (meth) acrylic acid in the second stage. Tobe specific, the vicinity of the end point of the reaction (6 a-9) inthe first stage and the vicinity of the starting point of the reaction(9-6 a′) in the second stage have high temperatures. Thus, the reactionis inhibited in those portions and the process gas is cooled by the heatmedium flowing through the flow path to the shell, to thereby prevent anautooxidation reaction of (meth)acrolein. In this case, the reactiontubes in the vicinity of the intermediate tube plate 9 (6 a-9-6 a′ ofreaction tubes 1 b and 1 c) are not packed with the catalyst, and thereaction tubes are left as cavities or packed with a solid withoutreaction activity. The latter is desirable for improving characteristicsof heat transfer.

<Start Up Method of the Present Invention>

A gist of a start up method of the present invention is as follows. In ashell-tube type reactor circulating a heat medium which is solid atnormal temperature, and having reaction tubes and an introducing portand a discharging port of a fluid flowing outside the reaction tubes forremoving heat generated in the reaction tubes, the start up method ischaracterized by comprising: introducing a gas at a temperature in therange of 100 to 400° C. to the outside of the reaction tube to heat; andcirculating the heat medium heated outside the reaction tube.

Hereinafter, the start up method of the present invention will bedescribed with reference to the accompanying drawings. FIG. 13 is aprocess explanatory diagram showing an example of a preferable modeaccording to the start up method of the present invention.

The start up method of the present invention is a start up method for ashell-tube type reactor circulating a heat medium which is solid atnormal temperature and having reaction tubes and an introducing port anda discharging port of a fluid flowing outside the reaction tubes forremoving heat generated in the reaction tubes.

First, the shell-tube type reactor used in the start up method of thepresent invention is described. Any one of the conventionally knownreactors may be employed as the shell-tube type reactor as long as thereactor employed has reaction tubes and an introducing port and adischarging port of a fluid flowing outside the reaction tubes forremoving heat generated in the reaction tubes. Above all, a multitubereactor is preferable because the reactor provides a high reactionefficiency per a volume of the reactor.

A multitube reactor that can be used in the start up method of thepresent invention generally has the following structure. That is, tubeplates are arranged on the top and bottom in the shell and a pluralityof reaction tubes are equipped inside the shell with both ends of eachreaction tube supported and fixed by the tube plates. Furthermore, anintroducing port and a discharging port of a fluid flowing outside thereaction tubes of the shell are provided for removing heat generated inthe reaction tubes. In the start up method of the present invention,shields may also be equipped for dividing the inside of the shell intomultiple chambers.

Next, a description is given of a heat medium used as a fluid flowingoutside the reaction tubes in the start up method of the presentinvention. The solidifying point of the heat medium is typically in therange of 50 to 250° C., preferably in the range of 130 to 180° C.Representative examples of such a heat medium include niter. Niter isparticularly preferable because niter is excellent in thermal stabilityamong the heat media used for controlling temperature in a chemicalreaction and, in particular, has the most excellent stability to heatexchange at high temperatures ranging from 350 to 550° C.

Niter is the so-called molten salt and may adopt various compositions.Therefore, the solidifying point of niter varies depending on thecompositions. However, niter of any composition can be suitably used inthe start up method of the present invention as long as the niter has asolidifying point in the above range. Examples of a compound used assuch niter include sodium nitrate, sodium nitrite, and potassiumnitrate. Each of those compounds can be used alone or 2 or more types ofthem can be mixed before use.

Next, the characteristics of the start up method of the presentinvention will be described. In the start up method of the presentinvention, a gas at a temperature in the range of 100 to 400° C. isintroduced to the outside of the reaction tubes to previously heat theinside of the reactor to a temperature equal to or higher than thesolidifying point of the heat medium. That is, in the method describedin the above-mentioned unexamined publication, a gas for heating areactor is introduced into reaction tubes packed with a catalystwhereas, in the start up method of the present invention, the gas isintroduced to the outside of the reaction tubes. This is acharacteristic of the start up method of the present invention. A startup method for a reactor according to the start up method of the presentinvention does not adversely affect the catalyst. Preferable examples ofthe gas for heating a reactor include air.

Next, the above-mentioned heating method in the process shown in FIG. 13will be described. In FIG. 13, a reactor represented by referencenumeral (50) has a first chamber and a second chamber. In the exampleshown in the figure, a process gas is fed as a downflow while a heatmedium is fed in an upflow. Lines (L1, L2, L3, and L4) constitute aprocess line, and lines (L6, L7, L8, L9, L10, L12, L13, and L14)constitute a heat medium line. Lines (L15 and L16) constitute adischarge line used during heating. In the figure, symbols ◯●- and ●◯-each represent a spectacle blind (SB), so-called partition. An SB isinserted into tubing to open and close a flow path. The former symbolrepresents an opened state, and the latter symbol represents a closedstate.

First, an SB (61) is inserted into the line (L3) (that is, the flow pathis closed) to close the feed line, used in ordinary operation, to thereaction tube (catalyst layer) of the reactor (50). Then, an SB (62) andan SB (63) are detached from the line (L5) (that is, the flow path isopened) to establish a line by the shell of the reactor (50) consistingof line (L1)→blower (10)→line (L2)→line (L5)→line (L6)→heater (21)→line(L7) and line (L8)→tank (30)→line (L9). At this time, a valve (71) ofthe line (L5) is closed. Furthermore, an SB (64) of the line (L15) and avalve (72) of the line (L6) are opened to discharge the introduced gas.

Subsequently, the blower (10) is started, and the gas heated to atemperature in the range of 100 to 400° C. is introduced to the outsideof the reaction tube of the reactor (50) by using the heater (21). Thegas heats the reactor (50). The temperature inside the reactor (50) ispreferably equal to or higher than the solidifying point of the heatmedium subsequently circulated, and the temperature can be appropriatelyselected depending on the heat medium used. In general, it is sufficientto heat the shell of the reactor (50) to a temperature in the range of150 to 250° C. This is because a temperature of the shell within theabove range prevents resolidification of the heat medium even if theheat medium is fed after heating the shell since the heat medium has asolidifying point in the range of 50 to 250° C. At this time, it ispreferable to keep the reaction tube (catalyst side) in an airatmosphere.

Subsequently, the blower (10) is stopped. The SB (62) of the line (L5)and the SB (63) of the line (L15) are closed. The valve (72) of the line(L16) is opened. Pumps (41 and 42) are started to introduce a heatmedium into each of the first chamber (51) and second chamber (52) ofthe reactor (50) Then, the heat medium is circulated in each chamber byusing an attached pump (43) to increase the temperature inside eachchamber.

Each operation described above is preferably performed quickly,preferably within 1 hour. Too slow operation may cause resolidificationof a heat medium when introducing the heat medium because thetemperature of the shell decreases due to radiation of heat.

When heat exchange is performed by using a heat medium which is solid atnormal temperature, the total amount of the heat medium is oftenrecovered in the tank (30) after the use of the reactor (50). In such acase, the heat medium does not remain in the reactor (50) and is storedin the tank (30). Therefore, the heat medium in the tank (30) is heatedby heaters (22 and 23) to an extent that the fluidity of the heat mediumis ensured, and the heat medium is then introduced into the reactor(50).

The heat medium is introduced into the reactor (50) through 2 routes asdescribed below. That is, the heat medium is fed to the first chamber(51) by the heat medium pump (41) of the tank (30) via the lines (L13,L14, L6, and L7). In addition, the heat medium is fed to the secondchamber (52) by the heat medium pump (42) of the tank (30) through thelines (L12 and L10).

Then, the heat medium introduced into the reactor (50) is circulatedinside each chamber by the attached pump (43). This is because thetemperature inside the reactor (50) may not be increased to a targettemperature only by introducing and circulating the heat medium heatedin advance. In view of this, the heat medium is circulated, heated bythe heater (21), and then introduced into the reactor (50) again. Forexample, the heat medium is discharged from the first chamber (51) andthe line (L8) and is introduced into the reactor (50) by the pump (41)through the line (L7) via the heater (21).

In the case where the required temperature of the reactor (50) can beensured through circulation of the heat-medium as described above, theproduction of a target product can be started by feeding a raw materialgas to reaction tubes (catalyst side).

A start up method for a reactor according to the start up method of thepresent invention is particularly preferable as a start up method for areactor used in the production of, for example, acrylic acid,methacrylic acid, acrolein, or methacrolein. This is because of thefollowing reason. That is, acrylic acid or the like is a compoundproduced and used in a large amount, and a reactor becomes large inresponse to this. Therefore, it is particularly difficult to heat thereactor. The start up method of the present invention is particularlysuitable for heating during start up of a large-scale reactor.

Acrylic acid is produced by: feeding propylene, propane, acrolein, orthe like as a raw material gas to a conventionally known reactor packedwith an oxidation catalyst; and allowing to react through a vapor phasecatalytic oxidation reaction. In general, a raw material gas is allowedto coexist with given amounts of a molecular oxygen-containing gas andan inert gas and then a vapor phase catalytic oxidation reaction iscarried out. For instance, when propylene is used as a raw material gas,acrolein is produced first. Then, acrolein is oxidized through vaporphase catalytic oxidation to yield acrylic acid.

Conventionally known oxidation catalysts can be used as former stage andlatter stage catalysts in the 2-stage vapor phase catalytic oxidationreaction described above. Furthermore, a shape of the catalyst is notparticularly limited and may be spherical, columnar, cylindrical, andthe like. Furthermore, the catalyst may be diluted with a solid inertmaterial when the catalyst is packed. Examples of such a solid inertmaterial include α-alumina, alundum, mullite, carborundum, stainlesssteel, copper, aluminum, and ceramics.

In the present invention, it is possible to realize a more suitablevapor phase catalytic oxidation in the production of (meth) acroleinand/or (meth) acrylic acid by applying the above-mentioned first andsecond vapor phase catalytic oxidation methods and of the start upmethod of the present invention to the above-mentioned multitube reactorof the present invention.

That is, the vapor phase catalytic oxidation method using a multitubereactor of the present invention further comprising baffles connectingto the reaction tubes through connecting sites for changing a flow pathof a heat medium introduced into the shell; circulating the heat mediumthrough the outside of the of the reaction tubes; and feeding a rawmaterial gas into the reaction tubes packed with a catalyst, to therebyobtain a reaction product gas, the vapor phase catalytic oxidationmethod comprising, determining catalyst packing specifications in thereaction tubes so that catalyst layer peak temperature sites of thereaction tubes are not located at the connecting sites between thebaffles and the reaction tubes.

Such a vapor phase catalytic oxidation method is preferable forimproving life of the catalyst packed inside the reaction tubes,preventing an yield of a target compound decreasing, preventing hot spotformation effectively, and performing a stable operation over a longperiod of time, without clogging the reaction tubes.

Further, in the present invention, the above-mentioned second vaporphase catalytic oxidation method can also be applied to such a vaporphase catalytic oxidation method. That is, propylene, propane, orisobutylene, and/or (meth)acrolein is oxidized through vapor phasecatalytic oxidation with a molecular oxygen-containing gas by packing aMo—Bi catalyst and/or a Sb—Mo catalyst to the reaction tube in such amanner that activity increases from the process gas inlet to process gasoutlet of the reaction tube; and allowing a heat medium and a processgas to flow in a countercurrent.

Such a method for vapor phase catalytic oxidation method is preferablefor improving life of the catalyst packed inside the reaction tubes,preventing an yield of a target product decreasing, preventing hot spotformation effectively, and performing a stable operation over a longperiod of time, without clogging the reaction tubes, and reducing thetemperature of the process gas at the product discharging port of thereactor.

Further, in the present invention, the above-mentioned start up methodof the present invention can also be applied to such a vapor phasecatalytic oxidation method. That is, in a method comprising at least oneof those vapor phase catalytic oxidation methods, the multitube reactoris stared up by: introducing a gas at a temperature in the range of 100to 400° C. to the outside of the reaction tubes to heat; and circulatinga heated heat medium which is solid at normal temperature through theoutside of the reaction tubes.

Such a vapor phase catalytic oxidation method is preferable for startingup a reactor efficiently without affecting the activity of a catalystadversely.

Although each of the reactor of the present invention and the reactorused in the vapor phase catalytic oxidation method of the presentinvention is limited to a multitube reactor equipped with a plurality ofreaction tubes inside a single shell, the limitations are based on anindustrial usage form. The present invention can also be applied to asingle tube reactor and the single tube reactor also takes the sameeffect as those of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an example of a multitube reactor.

FIG. 2 is a perspective view of an example of baffles equipped inside amultitube reactor.

FIG. 3 is a perspective view of another example of baffles equippedinside a multitube reactor.

FIG. 4 is a view of the multitube reactor shown in FIG. 1 seen fromabove.

FIG. 5 is a sectional view of another example of a multitube reactor.

FIG. 6 is a fragmentary sectional view of an intermediate tube plate andthermal shields equipped inside the multitube reactor shown in FIG. 5.

FIG. 7 is a diagram showing an embodiment of a fixed bed multitubeheat-exchanger type reactor used in the first vapor phase catalyticoxidation method.

FIG. 8 is a diagram showing an embodiment of a fixed bed multitubeheat-exchanger type reactor used in the first vapor phase catalyticoxidation method.

FIG. 9 is a diagram showing an embodiment of a fixed bed multitubeheat-exchanger type reactor used in the first vapor phase catalyticoxidation method.

FIG. 10 is a diagram showing an embodiment of a fixed bed multitubeheat-exchanger type reactor used in the first vapor phase catalyticoxidation method.

FIG. 11 is a diagram illustrating a state at connecting sites of bafflesand reaction tubes of a fixed bed multitube heat-exchanger type reactorused in the first vapor phase catalytic oxidation method.

FIG. 12 is a diagram illustrating a state of connecting sites of bafflesand reaction tubes of a fixed bed multitube heat-exchanger type reactorused in the first vapor phase catalytic oxidation method.

FIG. 13 is a process explanation diagram showing an example of apreferable embodiment of a start up method of the present invention.

FIG. 14 is a schematic diagram illustrating Example 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be further described in detailby examples, but the present invention is not limited by the examples solong as not departing from the gist of the invention.

EXAMPLE 1

For an oxidation reaction of propylene, catalyst powder having acomposition (atomic ratio) ofMo(12)Bi(5)Ni(3)Co(2)Fe(0.4)Na(0.2)B(0.4)K(0.1)Si(24)O(x) was produced(oxygen composition x is a value determined from oxidation states of therespective metals) as a former stage catalyst.

The catalyst powder was molded in to ring-shaped catalysts having anouter diameter of 5 mmφ, an inner diameter of 2 mmφ, and a height of 4mm.

Two stainless steel tubes both having a length of 3,500 mm, andrespectively having an outside diameter of 30.57 mmφ, a wall-thicknessof 1.80 mm, and an outside diameter of 30.23 mmφ, a wall-thickness of2.10 mm were used as reaction tubes (nominal outside diameter of 30.40mmφ and nominal wall-thickness of 1.80 mm). Note that, an outsidediameter tolerance and a wall-thickness tolerance of the tubes are ±0.17mm (±0.56%) and +0.30 mm, −0 mm (+16.7%, −0%), respectively.

Further, a reactor used had a shell inner diameter of 100 mmφ.

A nitrates-mixed molten salt niter was used as a heat medium Hm, and theheat medium was fed from a side of bottom of the shell.

Temperature of the niter fed to the shell was defined as reactiontemperature. Further, a flow rate of the niter was adjusted so that atemperature difference between an outlet and inlet of the shell was 4°C.

Each of the reaction tubes was packed with 3,000 mm of the catalyst, anda raw material gas (Rg) containing 9 vol % propylene was fed from anupper portion of the shell at a gauge pressure of 75 kFa.

Temperature distributions in the reaction tubes were measured byinserting thereinto thermometers each having 10 points of measurement inan axial direction of the reaction tubes.

A reaction was conducted for 1 week at a heat medium Hm temperature of330° C. A propylene conversion and an yield were 97.5% and 91.0%,respectively, and the highest temperature of reaction catalyst layerswas 392° C.

The reaction was continued for 1 month maintaining the heat medium Hmtemperature at 330° C. The propylene conversion and the yield were 97.0%and 90.5%, respectively, and the highest temperature of the reactioncatalyst layers was 386° C.

EXAMPLE 2

Two stainless steel tubes both having a length of 3,500 mm, andrespectively having an outside diameter of 30.58 mmφ, a wall-thicknessof 1.80 mm, and an outside diameter of 30.22 mmφ, a wall-thickness of2.14 mm were used as the reaction tubes (nominal outside diameter of30.40 mmφ and nominal wall-thickness of 1.80 mm). Note that, the outsidediameter tolerance and the wall-thickness tolerance of the tubes are±0.18 mm (±0.59%) and +0.34 mm, −0 mm (+18.9%, −0%), respectively.

The reaction was conducted in the same manner as in Example 1 except forthe reaction tubes.

The reaction was conducted for 1 week at a heat medium Hm temperature of330° C. The propylene conversion and the yield were 97.2% and 90.0%,respectively, and the highest temperature of the reaction catalystlayers was 394° C.

The reaction was continued for 1 month maintaining the heat medium Hmtemperature at 330° C. The propylene conversion and the yield were 96.8%and 89.7%, respectively, and the highest temperature of the reactioncatalyst layers was 389° C.

EXAMPLE 3

Two stainless steel tubes both having a length of 3,500 mm, andrespectively having an outside diameter of 30.65 mm®, a wall-thicknessof 1.80 mm, and an outside diameter of 30.15 mm®, a wall-thickness of2.16 mm were used as the reaction tubes (nominal outside diameter of30.40 mmφ and nominal wall-thickness of 1.80 mm). Note that, the outsidediameter tolerance and the wall-thickness tolerance of the tubes are±0.25 mm (±0.82%) and +0.36 mm, −0 mm (+20%, −0%), respectively.

The reaction was conducted in the same manner as in Example 1 except forthe reaction tubes.

The reaction was conducted for 1 week at a heat medium Hm temperature of330° C. The propylene conversion and the yield were 97.4% and 89.9%,respectively, and the highest temperature of the reaction catalystlayers was 429° C.

The reaction was continued for 1 month maintaining the heat medium Hmtemperature at 330° C. The propylene conversion and the yield were 94.0%and 88.0%, respectively, and the highest temperature of the reactioncatalyst layers was 422° C.

As described above, improvement on life of the catalyst packed insidethe reaction tubes and prevention of yield reduction of the targetproduct could be realized by using the reaction tubes having an outsidediameter tolerance of ±0.62% and a thickness tolerance of +19% to −0%.

EXAMPLE 4

A fixed bed multitube heat-exchanger type reactor shown in FIG. 14 whichhas 20,000 stainless steel reaction tubes having an inner diameter of 27mm and a length of 5 m and double segment-type baffles for changing aflow path of the heat medium in the shell was used. Multi-pointthermocouples were provided to allow measurement of catalyst layertemperature in the reaction tubes. Niter was used as the heat medium.

The reaction tube provided in position A in FIG. 14 was packed withalumina balls to a height of 1.7 m, a mixture containing 70% of anMo—Bi—Fe catalyst prepared following a conventional procedure and 30% ofalumina balls in volume ratio to a height of 3 m thereon, and aluminaballs to a height of 0.3 m thereon.

A mixed gas consisting of 9 mol % of propylene, 71 mol % of air, 10 mol% of steam, nitroger, and the like was fed in downflow under conditionsof a contact time of 3 seconds. A temperature of the heat medium is 32°C. at this time.

The catalyst layer peak temperature site at this time was this side of abaffle (first baffle, that is, baffle higher in position of the bafflesshown in FIG. 14) and the catalyst layer peak temperature was 400° C.Pressure loss increases of the reaction tube after 1-year operation and2-year operation were 0.1 kPa and 0.15 kPa, respectively.

Here, the term “pressure loss increase” refers to a phenomenon ofpressure increase inside the reaction tubes caused by a carbonization ofreaction raw materials due to too high temperature to clog the reactiontubes. The pressure loss is determined by: feeding air or nitrogen ofthe same volume as the volume of gas fed during the reaction to therespective reaction tubes; and measuring the pressure of the reactiontube inlet.

EXAMPLE 5

The reaction tube provided in position B (next to A) in FIG. 14 waspacked with alumina balls to a height of 1.5 m, a mixture containing 70%of the same catalyst as in Example 4 and 30% of alumina balls in volumeratio to a height of 3 m thereon, and alumina balls to a height of 0.5 mthereon.

The catalyst layer peak temperature site at this time was at aconnecting site of the first baffle and the reaction tube, and thecatalyst layer peak temperature was 415° C. The pressure loss increaseof the reaction tube after 1-year operation was 0.5 kPa. The reactiontube was completely clogged after 2-year-operation, and the pressureloss increase could not be measured. As described above, the catalystlayer peak temperature site located at the connecting site causesexcessive reaction and clogging of the reaction tube because removal ofheat of reaction is insufficient, which is also apparent from highcatalyst layer peak temperature.

As is clear from Examples 4 and 5, the present invention can provide avapor phase catalytic oxidation method capable of effectively preventinghot spot formation and performing a stable operation over a long periodof time and with long catalyst life, without clogging the reaction tubesby determining catalyst packing specifications in the reaction tubes sothat the catalyst layer peak temperature sites inside the reaction tubesare not located at connecting sites between the baffles and the reactiontubes.

EXAMPLE 6

94 parts by weight of antimony paramolybdate was dissolved in 400 partsby weight of pure water by heating. Then, 7.2 parts by weight of ferricnitrate, 25 parts by weight of cobalt nitrate, and 38 parts by weight ofnickel nitrate were dissolved in 60 parts by weight of pure water byheating. The two solutions were mixed with sufficient stirring.

Next, a solution prepared by dissolving 0.85 parts by weight of boraxand 0.36 parts by weight of potassium nitrate in 40 parts by weight ofpure water under heating was added to the slurry. Then, 64 parts byweight of particulate silica was added to the slurry, and the whole wasmixed. Next, 58 parts by weight of bismuth subcarbonate mixed with 0.8wt % Mg in advance was added to the mixture, and the whole was mixedunder stirring. The slurry was subjected to drying by heating, and thento heat treatment in air at 300° C. for 1 hour. The obtained particulatesolid was molded into tablets having a diameter of 5 mm and a height of4 mm through tablet compression using a molding machine. The tabletswere then baked at 500° C. for 4 hours, to thereby obtain a former stagecatalyst.

The obtained catalyst was Mo—Bi mixed oxide having a composition ratioof catalyst powder of a composition ofMo(12)Bi(5)Ni(3)Co(2)Fe(0.4)Na(0.2)Mg(0.4)B(0.2)K(0.1)Si(24)O(x) (oxygencomposition x is a value determined from oxidation states of therespective metals).

The multitube reactor used in this example was the same as that shown inFIG. 1. To be specific, the multitube reactor which has a shell (innerdiameter of 4,500 mm) having 10,000 stainless steel reaction tubeshaving a length of 3.5 m and an inner diameter of 27 mm is used. Thereaction tubes were not provided in a circular opening region at acenter of the perforated disc-type baffle 6 a having an opening portionin the vicinity of a central portion of the shell. The baffles werearranged such that the perforated disc-type baffle 6 a having an openingportion in the vicinity of the central portion of the shell and theperforated disc-type baffle 6 b provided to form an opening portionbetween the baffle and the outer peripheral portion of the shell wereprovided at even interval in an order of 6 a-6 b-6 a, and an openingratio of each of the baffles was 18%.

A nitrates-mixed molten salt (niter) was used as a heat medium, and theheat medium was fed from a lower portion of the reactor.

The catalysts packed in the reaction tubes were prepared by mixing theformer stage catalyst and silica balls having a diameter of 5 mm and nocatalytic activity, to thereby adjust the catalytic activity. Thereaction tubes were packed with the catalysts so that the ratio ofcatalytic activity was 0.5, 0.7, and 1 from the reaction tube inlet.

The raw material gas was fed from an upper portion of the reactor,forming a countercurrent with the heat medium. A raw material gasconsisting of 9 mol % of propylene, 1.9 mol % of molecular oxygen, 9 mol% of water, and 80.1% of nitrogen was fed at a gauge pressure of 75 kPa(kilopascal). The temperature distributions in the reaction tubes weremeasured by inserting into the reaction tubes thermometers each having10 points of measurement in an axial direction of the reaction tubes.

The reaction was conducted for 1 week at a heat medium temperature of330° C. The propylene conversion was 97% and a total yield of acroleinand acrylic acid was 92%. The temperature of the niter fed was definedas the reaction temperature. The temperature difference of the niterbetween the inlet and outlet of the reactor was 4° C.

The propylene conversion and the yield were 96.8% and 91.9%respectively, after continuing the reaction for 1 month maintaining theheat medium temperature at 330° C.

The gas temperature at the reactor outlet was constant at about 330° C.during operation.

EXAMPLE 7

The reaction tubes were packed with catalysts in the same manner as inExample 6 using the catalysts used in Example 6.

The multitube reactor was used, which has a shell (inner diameter of5,000 mm) having 9,500 stainless steel reaction tubes having a length of3.5 m and an inner diameter of 27 mm. The reaction tubes were notprovided in a circular opening region at a center of the perforateddisc-type baffle 6 a having an opening portion in the vicinity of acentral portion of the shell. The baffles were the same as those used inExample 6, and were arranged such that the perforated disc-type baffle 6a having an opening portion in the vicinity of the central portion ofthe shell and the perforated disc-type baffle 6 b provided to form anopening portion between the baffle and the outer peripheral portion ofthe shell were provided at even interval in an order of 6 a-6 b-6 a, andan opening ratio of each of the baffles was 18%.

A nitrates-mixed molten salt (niter) was used as a heat medium, and thiswas fed from a lower portion of the reactor. The raw material gasconsisting of 9 mol % of propylene, 1.9 mol % of molecular oxygen, 9 mol% of water, and 80.1 mol % of nitrogen was fed from the lower portion ofthe reactor (raw material feed port 4 a) at a gauge pressure of 75 kPa(kilopascal), changing to a concurrent with the heat medium. Feedtemperature of the heat medium was adjusted to obtain a propyleneconversion of 97%, resulting in a feeding temperature of 333° C.

The yield was 91% 1 week after start of the operation, and the gastemperature at the reactor outlet was 337° C. at this time.

The reaction was continued, and after 10 days from the start of theoperation, the gas temperature at an outlet portion of the reactorincreased sharply from 337° C., and thus, the operation was stopped.After stopping the operation, the reactor was inspected. Black depositswere observed in the tube of the product discharging port 4 b, andanalysis thereof confirmed that the deposits were C contents.

As is clear from Examples 6 and 7, the process gas temperature can bereduced at the product discharging port of the reactor by packing thereaction tubes with the catalysts so that the catalytic activityincreases-from the process gas inlet to the process gas outlet ofreaction tubes.

EXAMPLE 8

The multitube reactor was started up by using: the process shown in FIG.13; niter as a heat medium composed of 40 wt % sodium nitrite, 7 wt %sodium nitrate, and 53 wt % potassium nitrate; and air as a gas forheating introduced outside the reactor. Note that, the niter was storedin a tank and was not remained inside the reactor before the start up.Further, the multitube reactor used was an oxidation reactor having aninner diameter of 4,500 mm and had a structure including 13,000 reactiontubes having a length of 4,000 mm supported by an upper tube plate and alower tube plate. Further, a shield was provided at a position 300 mmfrom a lower portion of the reactor to divide the reactor into twochambers.

First, SBs (61) and (62) of respective lines (L3) and (L5) wereswitched, to change a line from a blower (10) into a reactor (50), to aline from the blower (10) to a heater (21). The blower (10) was thenstarted. Air was fed at a rate of 6 t/hr to the heater (21) forpreheating to 250° C., and the heated air was fed to the oxidationreactor (50) via a line (L7) and/or line (L8) to a tank (30) and then toa line (L9).

The blower (10) was stopped when the temperature of the reactor (50)reached 230° C., and the above SBs were switched. Then, a heat mediumheated to 200° C. in advance by heaters (22) and (23) were fed from thetank (30) with pumps (41) and (42). The heat medium was fed to a firstchamber (51) via lines (L13), (L14), (L6), and (L7) with the pump (41).The heat medium was fed to a second chamber (52) via lines (L12) and(L10) with the pump (42).

A pump (43) was then started after the heat medium was introduced intothe reactor (50), to circulate the heat medium inside the first chamber(51). The temperature of the first chamber (51) was adjusted by feedingthe heat medium from the reactor (50) to the heater (21) via lines (L8),(L13), (L14), and (L6) and circulating the heat medium to the reactor(50) via line (L7) The temperature of the second chamber (52) wasadjusted with the heater (23) attached to the tank (30).

The heat medium temperatures of the first chamber (51) and the secondchamber (52) were 330° C. and 230° C., respectively, reachingpredetermined reaction temperatures. Thus, the heater (21) was stopped,and the start up was completed. The start up took 40 hours.

EXAMPLE 9

A shell and tube type reactor having the following structure was used.That is, the reactor had a stainless. steel double-tube reaction tubeswith an inner tube having an inner diameter of 24 mm and a length of 3.5m. The inner tube was packed with a catalyst having a composition ofMo(12)Bi(5)Ni(3)Co(2)Fe(0.4)Na(0.2)B(0.4)K(0.1)Si(24)O(x) (oxygencomposition x is a value determined from oxidation states of therespective metals). A region between the inner tube and an outer tubewas filled with niter as the heat medium so that uniform temperature wasmaintained by stirring.

Instrumented air was fed to the reactor at a rate of 1 Nl/hr and theshell was maintained at 250° C. for 40 hours. Then, the niter at 330° C.was circulated, and the raw material gas containing 9 vol % of propyleneas a raw material was fed to the reactor. The propylene conversion was97% and the total yield of acrolein and acrylic acid was 92%.

EXAMPLE 10

The reaction was conducted in the same manner as in Example 9 exceptthat nitrogen heated to 250° C. was fed to the inner tube (catalystlayer) at a rate of 20 l/hr for 40 hours. Here, the niter temperaturehad to be increased to 340° C. to obtain a propylene conversion of 97%.

EXAMPLE 11

The reaction was conducted in the same was as in Example 9 except thatair heated to 250° C. was fed to the inner tube (catalyst layer) at arate of 20 Nl/hr for 40 hours. In Example 11, the activity of thecatalyst changed provoking a reaction out of control, and the reactionhad to be stopped.

As is clear from Examples 8, 9, 10, and 11, the reactor can be startedup effectively without adversely affecting the catalytic activity by:introducing heated gas to the outside of the reaction tubes packed withthe catalysts to heat the catalyst; and circulating the heated heatmedium to the outside of the reaction tubes.

Industrial Applicability

According to the present invention, in a multitube reactor and a methodfor producing (meth) acrylic acid which uses the reactor, tube productshaving a nominal outside diameter tolerance and a nominal wall-thicknesstolerance of ±0.62% and +19% to −0% respectively, particularlypreferably ±0.56% and +17% to −0% respectively, which are more rigorousthan the tolerances of the present engineering specification JIS orASTM, were used as the reaction tubes equipped inside the shell of thereactor. As a result, the present invention enables (meth)acrylic acidproduction from propylene or isobutylene while effectively preventing areaction out of control and advanced catalyst deterioration andproducing (meth)acrylic acid stably at a high yield over a long periodof time.

The present invention provides a vapor phase catalytic oxidation methodof obtaining a reaction product gas capable of effectively preventinghot spot formation and performing a stable operation at a high yield ofa reaction product gas over a long period of time and with long catalystlife, without clogging the reaction tubes by: using a fixed bedmultitube heat-exchanger type reactor having a plurality of reactiontubes and baffles for changing a flow path of the heat medium;circulating the heat medium through the outside of the reaction tubes;and feeding the raw material gas inside the reaction tubes packed with acatalyst.

The present invention provides a multitube reactor and a vapor phasecatalytic oxidation method capable of reducing the product temperature,preventing autooxidation of the product, obtaining the product in highyield, and preventing equipment breakdown due to abnormal increase oftemperature through autooxidation by: allowing the heat mediumcirculating to flow in the multitube reactor and the process gas in acountercurrent, that is, in opposite directions; and packing thereaction tubes with a specific catalyst.

The present invention provides an efficient start up method for ashell-tube type reactor circulating a heat medium which is solid atnormal temperature, without adversely affecting the catalytic activity.The present invention is significantly valuable industrially.

Further, the present invention can actualize the multitube reactor orthe vapor phase catalytic oxidation method employing the multitubereactor exerting the plurality of above-mentioned significant effects.

1-4. (canceled)
 5. A vapor phase catalytic oxidation method comprising:providing a multitube reactor comprising a plurality of reaction tubeshaving a catalyst packed therein, and a shell equipped with the reactiontubes inside and into which a heat medium flowing outside the reactiontubes is introduced, wherein the reaction tubes are selected from tubeshaving same nominal outside diameter and same nominal wall-thickness, anoutside diameter tolerance of ±0.62%, and a wall-thickness tolerance of+19% to −0%, which further comprises baffles connected to the reactiontubes through connecting sites for changing a flow path of a heat mediumintroduced into the shell; circulating the heat medium through theoutside of the reaction tubes; and feeding a reaction raw material gasinside the reaction tubes packed with a catalyst to obtain reactionproduct gas; wherein the method comprises setting catalyst packingspecifications in the reaction tubes so that catalyst layer peaktemperature sites of the reaction tubes are not located at theconnecting sites between the baffles and the reaction tubes.
 6. A vaporphase catalytic oxidation method comprising: providing a multitubereactor comprising a plurality of reaction tubes having a catalystpacked therein, and a shell equipped with the reaction tubes inside andinto which a heat medium flowing outside the reaction tubes isintroduced, wherein the reaction tubes are selected from tubes havingsame nominal outside diameter and same nominal wall-thickness, anoutside diameter tolerance of ±0.56%, and a wall-thickness tolerance of+17% to −0%, which further comprises baffles connected to the reactiontubes through connecting sites for changing a flow path of a heat mediumintroduced into the shell; circulating the heat medium through theoutside of the reaction tubes; and feeding a reaction raw material gasinside the reaction tubes packed with a catalyst to obtain reactionproduct gas; wherein the method comprises setting catalyst packingspecifications in the reaction tubes so that catalyst layer peaktemperature sites of the reaction tubes are not located at theconnecting sites between the baffles and the reaction tubes.
 7. Thevapor phase catalytic oxidation method according to claim 5, wherein themethod comprises: packing the reaction tubes with a Mo—Bi catalystand/or Sb—Mo catalyst so that an activity increases from a process gasinlet to a process gas outlet of the reaction tubes; allowing the heatmedium and the process gas to flow in a countercurrent; and oxidizingpropylene, propane, or isobutylene, and/or (meth)acrolein through vaporphase catalytic oxidation with a molecular oxygen-containing gas.
 8. Thevapor phase catalytic oxidation method according to claim 6, wherein themethod comprises: packing the reaction tubes with a Mo—Bi catalystand/or Sb—Mo catalyst so that an activity increases from a process gasinlet to a process gas outlet of the reaction tubes; allowing the heatmedium and the process gas to flow in a countercurrent; and oxidizingpropylene, propane, or isobutylene, and/or (meth)acrolein through vaporphase catalytic oxidation with a molecular oxygen-containing gas.
 9. Thevapor phase catalytic oxidation method according to claim 5, wherein themethod comprises: heating the reaction tubes through introduction of agas having temperature of 100 to 400° C. outside the reaction tubes; andcirculating the heat medium which is solid at normal temperature outsidethe heated reaction tubes to start up the multitube reactor.
 10. Thevapor phase catalytic oxidation method according to claim 6, wherein themethod comprises: heating the reaction tubes through introduction of agas having temperature of 100 to 400° C. outside the reaction tubes; andcirculating the heat medium which is solid at normal temperature outsidethe heated reaction tubes to start up the multitube reactor.
 11. A vaporphase catalytic oxidation method comprising: using a fixed bed multitubeheat-exchanger type reactor having a plurality of reaction tubes andbaffles connected to the reaction tubes through connecting sites forchanging a flow path of a heat medium flowing outside the reactiontubes; circulating the heat medium through the outside of the reactiontubes; feeding a reaction raw material gas inside the reaction tubespacked with a catalyst to obtain a reaction product gas, wherein themethod comprises setting catalyst packing specifications in the reactiontubes so that catalyst layer peak temperature sites of the reactiontubes are not located at the connecting sites between the baffles andthe reaction tubes.
 12. The vapor phase catalytic oxidation methodaccording to claim 11, wherein layers having different catalyst packingspecifications are provided with at least two or more in one reactiontube.
 13. The vapor phase catalytic oxidation method according to claim11, wherein items for setting the catalyst packing specificationscomprise a type of the catalyst, an amount of the catalyst, a form ofthe catalyst, a method for diluting the catalyst, and lengths ofreaction zones.
 14. The vapor phase catalytic oxidation method accordingto claim 11, wherein the method comprises oxidizing propane, propylene,and/or isobutylene with molecular oxygen through the vapor phasecatalytic oxidation method to produce (meth)acrylic acid.
 15. A vaporphase catalytic oxidation method comprises: using a multitube reactorwhich comprises: a cylindrical shell having a raw material feed port anda product discharging port; a plurality of ring-shaped tubes arranged onan outer periphery of the cylindrical shell for introducing ordischarging a heat medium into or from the cylindrical shell; acirculating device connecting the plurality of the ring-shaped tubes oneanother; a plurality of reaction tubes restrained by a plurality of tubeplates of the reactor and comprising a catalyst; and a plurality ofbaffles provided in a longitudinal direction of the reactor and forchanging a direction of the heat medium introduced into the cylindricalshell; oxidizing propylene, propane, or isobutylene, and/or(meth)acrolein through vapor phase catalytic oxidation with a molecularoxygen-containing gas to obtain (meth)acrolein and/or (meth)acrylicacid,; wherein the method comprises, packing a Mo—Bi catalyst and/orSb—Mo catalyst in the reaction tubes so that an activity increases froma process gas inlet to a process gas outlet of the reaction tubes; andallowing the heat medium and the process gas to flow in acountercurrent.
 16. The vapor phase catalytic oxidation method accordingto claim 15, wherein the Mo—Bi catalyst is represented by the followinggeneral formula (I) and the Sb—Mo catalyst is represented by thefollowing general formula (II):Mo_(a)W_(b)Bi_(c)Fe_(d)A_(e)B_(f)C_(g)D_(h)E_(i)O_(j)   (I) (wherein, Morepresents molybdenum; W represents tungsten; Bi represents bismuth; Ferepresents iron; A represents at least one type of element chosen fromnickel and cobalt; B represents at least one type of element selectedfrom the group consisting of sodium, potassium, rubidium, cesium, andthallium; C represents at least one type of element selected fromalkaline earth metals; D represents at least one type of elementselected from the group consisting of phosphorus, tellurium, antimony,tin, cerium, lead, niobium, manganese, arsenic, boron, and zinc; Erepresents at least one type of element selected from the groupconsisting of silicon, aluminum, titanium, and zirconium; O representsoxygen; a, b, c, d, e, f, g, h, i, and j represent atomic ratios of Mo,W, Bi, Fe, A, B, C, D, E, and O respectively; and if a=12, 0≦b≦10,0<c≦10, 0<d≦10, 2≦e≦15, 0<f≦10, 0≦g≦10, 0≦h≦4, and 0≦i≦30; and j is avalue determined from oxidation states of the respective elements); andSb_(k)MO_(l)(V/Nb)_(m)X_(n)Y_(p)Si_(q)O_(r)   (II) (wherein, Sbrepresents antimony; Mo represents molybdenum; V represents vanadium; Nbrepresents niobium; X represents at least one type of element selectedfrom the group consisting of iron (Fe), cobalt (Co), nickel (Ni), andbismuth (Bi); Y represents at least one type of element chosen fromcopper (Cu) and tungsten (W); Si represents silicon; O representsoxygen; (V/Nb) represents V and/or Nb; k, l, m, n, p, q, and r representatomic ratios of Sb, Mo, (V/Nb), X, Y, Si, and O respectively; and1≦k≦100, 1≦l≦100, 0.1≦m≦50, 1≦n≦100, 0.1≦p≦50, 1≦q≦100; and r is a valuedetermined from oxidation states of the respective elements). 17-18.(canceled)